Excel Export Issue

In the below code i am exporting excel from grid view when i export only first page of gridview is binded in excel not remaining page and the value likes 1.000 are changed to 1 i want 1.000 to be in excel.Please help me to overcome this issue.

  HtmlForm form = new HtmlForm();
                    Response.Clear();
                    Response.Buffer = true;
                    Response.Charset = "";
                    Response.AddHeader("content-disposition", string.Format("attachment;filename={0}", "ProductValuationReport.xls"));
                    Response.ContentType = "application/ms-excel";
                    StringWriter sw = new StringWriter();
                    HtmlTextWriter hw = new HtmlTextWriter(sw);
                    GridOpenstk.AllowPaging = false;
                    GridOpenstk.HeaderStyle.ForeColor = System.Drawing.Color.Black;

                    form.Attributes["runat"] = "server";
                    form.Controls.Add(GridOpenstk);
                    this.Controls.Add(form);
                    form.RenderControl(hw);
                    string style = @"<style> .textmode { mso-number-format:\@;}</style>";
                    Response.Write(style);
                    Response.Output.Write(sw.ToString());
                    Response.Flush();
                    Response.End();