how to merged cells in centre i send the code help me

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C#

private void LoadDetails()
{
try
{
SqlDataReader Xldr;
Excel.Application xlApp;
Excel.Workbook xlWorkBook;
Excel.Worksheet xlWorkSheet;
object misValue = System.Reflection.Missing.Value;
Excel.Range chartRange;
xlApp = new Excel.ApplicationClass();
xlWorkBook = xlApp.Workbooks.Add(misValue);
xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);
Int32 xlRow;

//load the course details
sql = "select course FROM Tb_SCh_TIme_Table group by course order by course ";
dr = GFun.ReadSql(sql);
xlRow = 3;
while (dr.Read())
{
//ColName.Name = dr[0].ToString().Trim();
xlWorkSheet.Cells[xlRow,1] = dr[0].ToString().Trim();
chartRange = xlWorkSheet.get_Range("A" + xlRow, "E" + xlRow);
//chartRange.Cells.HorizontalAlignment = xl
chartRange.MergeCells = true;
//chartRange.Cells.Font = FontStyle.Bold;
chartRange.Cells.Font.Bold = true ;


xlRow = xlRow + 1;
xlWorkSheet.Cells[xlRow, 1] = "Date";
xlWorkSheet.Cells[xlRow, 2] = "Session 1";
xlWorkSheet.Cells[xlRow, 3] = "Session 2";
xlWorkSheet.Cells[xlRow, 4] = "Session 3";
xlWorkSheet.Cells[xlRow, 5] = "Session 4";
xlRow = xlRow + 1;

sql = "select * FROM Tb_SCh_TIme_Table P PIVOT ";
sql = sql + "(MAX(Faculty_Code) FOR Session IN ([1],[2],[3] ,[4])) AS PVT ";
sql = sql + " where course = '" + dr[0].ToString().Trim() + "' order by date";
Xldr = GFun.ReadSql(sql);
while (Xldr.Read())
{
xlWorkSheet.Cells[xlRow, 1] = Xldr[1].ToString();
xlWorkSheet.Cells[xlRow, 2] = Xldr[3].ToString();
xlWorkSheet.Cells[xlRow, 3] = Xldr[4].ToString();
xlWorkSheet.Cells[xlRow, 4] = Xldr[5].ToString();
xlWorkSheet.Cells[xlRow, 5] = Xldr[6].ToString();
if (Xldr[4].ToString().Trim() == "")
{

}

Xldr.Close();
xlRow = xlRow + 2;
}
dr.Close();

xlWorkBook.SaveAs("csharp.net-informations.xls", Excel.XlFileFormat.xlWorkbookNormal, misValue, misValue, misValue, misValue, Excel.XlSaveAsAccessMode.xlExclusive, misValue, misValue, misValue, misValue, misValue);
xlWorkBook.Close(true, misValue, misValue);
xlApp.Quit();
releaseObject(xlApp);
releaseObject(xlWorkBook);
releaseObject(xlWorkSheet);
MessageBox.Show("File created !");
}
catch (Exception Ex1)
{
MessageBox.Show(Ex1.ToString(), "Error");
}
}


from my code i merge the cell but i want the merge cells to be in CENTRE. from my code please tell how can i do.