Open new Window after inserting ASP.Net GridView record into database using C#

I have GridView. When i have one row in GridView then save value into database, it redirect page one time, if i have two rows in GridView, then it redirect two time, which should not be.

Just i want to redirect one time

protected void btn_Save_Click(object sender, EventArgs e)
{
    if (txtentdate.Text == "")
    {
        Response.Write("<script language='javascript'>alert('Please Input Date');</script>");
        txtentdate.Focus();
    }
 
    else if (ddldebit.SelectedValue == "0")
    {
        Response.Write("<script language='javascript'>alert('Please Select Bank ');</script>");
    }
    else if (txtchequino.Text == "")
    {
        Response.Write("<script language='javascript'>alert('Please Input Cheque No.');</script>");
        txtchequino.Focus();
    }
    else if (txtchequdate.Text == "")
    {
        Response.Write("<script language='javascript'>alert('Please Input Cheque Date');</script>");
        txtchequdate.Focus();
    }
    else if (txtamount.Text == "")
    {
        Response.Write("<script language='javascript'>alert('Please Input Amount');</script>");
        txtamount.Focus();
    }
 
    //decimal totalDebit = Convert.ToDecimal(hfDebit.Value);
    //decimal totalCredit = Convert.ToDecimal(txtamount.Text);
 
    else if (gvtrans.Rows.Count == 0)
    {
        Response.Write("<script language='javascript'>alert('Please Select head');</script>");
    }
 
    else if (Convert.ToDecimal(hfDebit.Value) != Convert.ToDecimal(hfCredit.Value))
    {
        Response.Write("<script language='javascript'>alert('Debit and Credit Amount must be Equal');</script>");
    }
    else
    {
        using (SqlCommand cmd1 = new SqlCommand("Sp_Insert_tbl_Transection", con))
        {
            loadtransID();
            cmd1.CommandType = CommandType.StoredProcedure;
            cmd1.Parameters.AddWithValue("@Trans_ID", lbid.Text);
 
            cmd1.Parameters.AddWithValue("@Trans_Date", txtentdate.Text);
            cmd1.Parameters.AddWithValue("@Trans_Type_ID", 1);
            cmd1.Parameters.AddWithValue("@Level_Five_ID_D", DBNull.Value);
            cmd1.Parameters.AddWithValue("@Level_Five_ID_C", ddldebit.SelectedValue);
            cmd1.Parameters.AddWithValue("@Trans_Remarks", txtremarks.Text);
            cmd1.Parameters.AddWithValue("@trans_Container_No", string.IsNullOrEmpty(txtcontainer.Text) ? (object)DBNull.Value : txtcontainer.Text);
            cmd1.Parameters.AddWithValue("@Trans_Amount", txtamount.Text.Trim());
            cmd1.Parameters.AddWithValue("@Cheque_No", txtchequino.Text.Trim());
 
            cmd1.Parameters.AddWithValue("@Cheque_Date", txtchequdate.Text);
            cmd1.Parameters.AddWithValue("@Emp_ID", lbempid.Text);
            cmd1.Parameters.AddWithValue("@E_Date", DateTime.Now.ToString());
            cmd1.Parameters.AddWithValue("@E_Time", DateTime.Now.ToString("hh:mm:ss"));
 
            con.Open();
            cmd1.ExecuteNonQuery();
            con.Close();
        }
            foreach (GridViewRow row in gvtrans.Rows)
            {
                TextBox transId = row.FindControl("txtcode") as TextBox;
                DropDownList ddltype = row.FindControl("ddltype") as DropDownList;
                TextBox debit = row.FindControl("txtDebit") as TextBox;
                 TextBox credit = row.FindControl("txtCredit") as TextBox;
                DropDownList ddlfourdr = row.FindControl("ddlfourdr") as DropDownList;
 
                TextBox remarks = row.FindControl("txtremarks") as TextBox;
 
 
            string message = "Saved successfully.";
            string script = "window.onload = function(){ alert('";
            script += message;
            script += "');";
            script += "window.location = '";
            script += Request.Url.AbsoluteUri;
            script += "'; }";
            ClientScript.RegisterStartupScript(this.GetType(), "SuccessMessage", script, true);
 
            string Url = "/Bpprt.aspx?ID=" + lbid.Text;
            Response.Write("<script language='javascript'>window.open('" + Url + "','_blank','');");
            Response.Write("</script>");
 
                if (transId.Text == "")
                {
                    Response.Write("<script language='javascript'>alert('Please Select Head');</script>");
                }
                else if (debit.Text != "0")
                {
                    using (SqlCommand cmd1 = new SqlCommand("Sp_Insert_tbl_Transection", con))
                    {
                        cmd1.CommandType = CommandType.StoredProcedure;
                        cmd1.Parameters.AddWithValue("@Trans_ID", lbid.Text);
 
                        cmd1.Parameters.AddWithValue("@Trans_Date", txtentdate.Text);
                        cmd1.Parameters.AddWithValue("@Trans_Type_ID", 1);
                        cmd1.Parameters.AddWithValue("@Level_Five_ID_D", ddlfourdr.SelectedValue);
                        cmd1.Parameters.AddWithValue("@Level_Five_ID_C", DBNull.Value);
                        cmd1.Parameters.AddWithValue("@Trans_Remarks", txtremarks.Text);
                        cmd1.Parameters.AddWithValue("@R_Remarks", remarks.Text);
                        cmd1.Parameters.AddWithValue("@trans_Container_No", string.IsNullOrEmpty(txtcontainer.Text) ? (object)DBNull.Value : txtcontainer.Text);
                        cmd1.Parameters.AddWithValue("@Trans_Amount", debit.Text.Trim());
                        cmd1.Parameters.AddWithValue("@Cheque_No", txtchequino.Text.Trim());
 
                        cmd1.Parameters.AddWithValue("@Cheque_Date", txtchequdate.Text);
                        cmd1.Parameters.AddWithValue("@Emp_ID", lbempid.Text);
                        cmd1.Parameters.AddWithValue("@E_Date", DateTime.Now.ToString());
                        cmd1.Parameters.AddWithValue("@E_Time", DateTime.Now.ToString("hh:mm:ss"));
 
 
                    con.Open();
                    cmd1.ExecuteNonQuery();
                    con.Close();
 
                }
            }
            else if (credit.Text != "0")
            {
                using (SqlCommand cmd1 = new SqlCommand("Sp_Insert_tbl_Transection", con))
                {
                    cmd1.CommandType = CommandType.StoredProcedure;
                    cmd1.Parameters.AddWithValue("@Trans_ID", lbid.Text);
                    cmd1.Parameters.AddWithValue("@Trans_Date", txtentdate.Text);
                    cmd1.Parameters.AddWithValue("@Trans_Type_ID", 1);
                    cmd1.Parameters.AddWithValue("@Level_Five_ID_C", ddlfourdr.SelectedValue);
                    cmd1.Parameters.AddWithValue("@Level_Five_ID_D", DBNull.Value);
                    cmd1.Parameters.AddWithValue("@Trans_Remarks", txtremarks.Text);
                    cmd1.Parameters.AddWithValue("@R_Remarks", remarks.Text);
                    cmd1.Parameters.AddWithValue("@trans_Container_No", string.IsNullOrEmpty(txtcontainer.Text) ? (object)DBNull.Value : txtcontainer.Text);
                    cmd1.Parameters.AddWithValue("@Trans_Amount", credit.Text.Trim());
                    cmd1.Parameters.AddWithValue("@Cheque_No", txtchequino.Text.Trim());
 
                    cmd1.Parameters.AddWithValue("@Cheque_Date", txtchequdate.Text);
                    cmd1.Parameters.AddWithValue("@Emp_ID", lbempid.Text);
                    cmd1.Parameters.AddWithValue("@E_Date", DateTime.Now.ToString());
                    cmd1.Parameters.AddWithValue("@E_Time", DateTime.Now.ToString("hh:mm:ss"));
 
                    con.Open();
                    cmd1.ExecuteNonQuery();
                    con.Close();                          
                }
            }
        }
    }
}