about datagridview columns header width

PART 1: WHERE RESULT DOES NOT SHOW CORRECT
private void frm_Load(object sender, EventArgs e)
  {
 showSummary();
 }
private void showSummary()
  {
  lblHeaderSchedule.Text = "  \"Manual Schedule\" Summary  ";
  dgvSummary.Rows.Clear();
  dgvSummary.Columns.Clear();
  if (dgvSchedules.RowCount > 0)
  {
  int planNo = Convert.ToInt32(dgvSchedules.CurrentRow.Cells["PLANNO"].Value.ToString());
 
  DataTable dtHead = new DataTable();
 
  dtHead = iyms.GetPlanParameters(planNo);
  StrFields = dba.dbReturnFields(dtHead);
 
  dgvSummary.Columns.Add("SeqNo", "SEQNO");
  dgvSummary.Columns.Add("Specific", "");
  dgvSummary.Columns.Add("SubPlan", "SUBPLAN");
  dgvSummary.Columns.Add("noOfCoils", "TOTAL COILS");
  for (int i = 0; i < dtHead.Rows.Count; i++)
  dgvSummary.Columns.Add(dtHead.Rows[i][0].ToString(), dtHead.Rows[i][0].ToString());
 
  dgvSummary.Columns[0].Width = 57;
  dgvSummary.Columns[1].Width = 30;
  for (int i = 2; i < dgvSummary.ColumnCount; i++)
  {
  dgvSummary.Columns[i].Width = ((dgvSummary.Width - 87) / (dgvSummary.ColumnCount - 2)) - 1;
  }
 
  DataTable dtPlanGroup = new DataTable();
 
  dtPlanGroup = iyms.GetGroupNo(planNo, "seqno");
  DataTable dtTotalCoils = new DataTable();
  DataTable dtValue = new DataTable();
  string strTemp;
  for (int i = 0; i < dtPlanGroup.Rows.Count; i++)
  {
  //string str = "";
 
  //DataTable dtTotalCoils = new DataTable();
  dtTotalCoils = iyms.GetDetailsOfSpecificPlanAndGroup(planNo, Convert.ToInt32(dtPlanGroup.Rows[i][0].ToString()));
 
  //DataTable dtValue = new DataTable();
  dtValue = iyms.GetParameterWithValueOfSpecificPlanAndGroup(planNo, Convert.ToInt32(dtPlanGroup.Rows[i][0].ToString()));
  //string strTemp;
  dgvSummary.Rows.Add();
  dgvSummary.Rows[i].Cells[0].Value = dtTotalCoils.Rows[0][0].ToString();
  dgvSummary.Rows[i].Cells[1].Value = dtTotalCoils.Rows[0][2].ToString();
  if (dgvSummary.Rows[i].Cells[1].Value.ToString() == "1")
  dgvSummary.Rows[i].Cells[1].Value = "";
  else
  {
  dgvSummary.Rows[i].Cells[1].Value = "*";
  dgvSummary.Rows[i].Cells[1].Style.ForeColor = Color.Red;
  }
  dgvSummary.Rows[i].Cells[2].Value = Convert.ToInt32(dtPlanGroup.Rows[i][0].ToString());
  dgvSummary.Rows[i].Cells[3].Value = dtTotalCoils.Rows[0][1].ToString();
  for (int j = 0; j < dtHead.Rows.Count; j++)
  {
  dgvSummary.Rows[i].Cells[j + 4].Value = "X";
  dgvSummary.Rows[i].Cells[j + 4].Style.ForeColor = Color.Red;
  strTemp = "";
  for (int k = 0; k < dtValue.Rows.Count; k++)
  {
  if (dtValue.Rows[k][0].ToString() == dtHead.Rows[j][0].ToString())
  {
  strTemp = dtValue.Rows[k][1].ToString();
  dgvSummary.Rows[i].Cells[j + 4].Value = strTemp;
  dgvSummary.Rows[i].Cells[j + 4].Style.ForeColor = Color.Black;
  }
  }
 
  }

  }
  if (dgvSummary.RowCount > 0)
  {
 
  for (int i = 0; i < dgvSummary.ColumnCount; i++)
  {
  dgvSummary.Columns[i].SortMode = DataGridViewColumnSortMode.NotSortable;
  dgvSummary.Columns[i].DefaultCellStyle.Alignment = DataGridViewContentAlignment.MiddleCenter;
  }
 
  }
 
 
  int m = 235, l = 90, n = 190;
 
  if (dgvSummary.RowCount > 0)
  {
  for (int i = 0; i < dgvSummary.RowCount; i++)
  {
  m = m - 20;
  l = l + 20;
  n = n - 20;
  if ((m > 255 || m < 20)) m = 255;//235;
  if ((l > 255 || l < 20)) l = 100;//90;
  if ((n > 255 || n < 20)) n = 210;//190;
  dgvSummary.Rows[i].Cells[0].Style.BackColor = Color.FromArgb(n, l, m);

  }
 
  dgvSummary.CurrentCell = null;
  }
 
  dtHead.Dispose();
  dtPlanGroup.Dispose();
  dtTotalCoils.Dispose();
  dtValue.Dispose();
  }
  }

PART 2: IF I CALLED THIS METHOD INSIDE ANOTHER GRID'S CELL CLICK EVENT THEN RESULT DISPLAYED CORRECT
private void dgvSchedules_CellClick(object sender, DataGridViewCellEventArgs e)
{
  if (dgvSchedules.RowCount == 0)
  return;
 
  if (dgvSchedules.CurrentRow.Cells["SOURCE"].Value.ToString() == "MANUAL")
  {
  showSummary();
  }
}