Insert Record two time in table

suppose sir,
I have two dropdown and one textbox.
from dropdown1 I was select 8AM
from dropdown2 I was select 9AM
In textbox we enter value like Task1.
after i click on save button.so this 3 record inserted into database.That i have implemented.now when I will refresh the page from (f5) that time this same record again inserted into databse

Ok sir..I will share my code..
protected void LinkButton2_Click(object sender, EventArgs e)
{

if (ViewState["CurrentTable"] != null)
{
DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
DataRow drCurrentRow = null;
if (dtCurrentTable.Rows.Count > 0)
{
drCurrentRow = dtCurrentTable.NewRow();
drCurrentRow["RowNumber"] = dtCurrentTable.Rows.Count + 1;
dtCurrentTable.Rows.Add(drCurrentRow);
ViewState["CurrentTable"] = dtCurrentTable;
TimeSpan time = new TimeSpan();
for (int i = 0; i < dtCurrentTable.Rows.Count - 1; i++)
{
DropDownList ddl1 = (DropDownList)GridView1.Rows[i].Cells[1].FindControl("DropDownList1");
DropDownList ddl2 = (DropDownList)GridView1.Rows[i].Cells[2].FindControl("DropDownList2");
dtCurrentTable.Rows[i]["Column1"] = ddl1.SelectedItem.Text;
dtCurrentTable.Rows[i]["Column2"] = ddl2.SelectedItem.Text;
TextBox box1 = (TextBox)GridView1.Rows[i].Cells[3].FindControl("TextBox1");
dtCurrentTable.Rows[i]["Column3"] = box1.Text;
Label lbl1 = (Label)GridView1.Rows[i].Cells[4].FindControl("Label2");
System.DateTime time1 = new System.DateTime();
System.DateTime time2 = new System.DateTime();
time1 = DateTime.Parse(ddl1.SelectedItem.Text);
time2 = DateTime.Parse(ddl2.SelectedItem.Text);
TimeSpan ts = time2.Subtract(time1);
lbl1.Text = Convert.ToString(ts);
time = time + ts;
// Label3.Text = Convert.ToString(time);
dtCurrentTable.Rows[i]["Column4"] = lbl1.Text;

DailyTimeSheetTrackers objTimeTracker = new DailyTimeSheetTrackers();

objTimeTracker = new DailyTimeSheetTrackers();
objTimeTracker.EmployeeId = UserLog.UserId;
objTimeTracker.CreateDateTime = StaticKeys.getLocaleDatefromUTC();
objTimeTracker.CreateUserId = UserLog.UserId;
objTimeTracker.TaskTimeIn = DateTime.Parse(ddl1.SelectedItem.Text);
objTimeTracker.TaskTimeOut = DateTime.Parse(ddl2.SelectedItem.Text);
objTimeTracker.TaskDescription = box1.Text;
objTimeTracker.Status = true;
if (!(new DailyTimeSheetTrackersFactory()).Insert(objTimeTracker))
{
//ltrError.Text = objTimeTracker.BrokenRulesList.ToString();
//dvError.Visible = true;
return;
}

}
}
//Insert();
}