Error Updating data in ASP.NET

protected void UpdateService(object sender, GridViewUpdateEventArgs e)
        {
            int ServiceId = Convert.ToInt32(((Label)GridView1.Rows[e.RowIndex].FindControl("lblServiceID")).Text);
            string ServiceName = ((TextBox)GridView1.Rows[e.RowIndex].FindControl("txtService")).Text;
            decimal Rate = Convert.ToDecimal(((TextBox)GridView1.Rows[e.RowIndex].FindControl("txtRate")).Text);
            string ParentService = ((DropDownList)GridView1.Rows[e.RowIndex].FindControl("ddlParentService")).SelectedItem.Text;
            string GrandParentService = ((DropDownList)GridView1.Rows[e.RowIndex].FindControl("ddlGrandParentService")).SelectedItem.Text;
                                   
            SqlConnection con = new SqlConnection(strConnString);
            SqlCommand cmd = new SqlCommand();
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "update Service set ServiceName=@ServiceName,Rate=@Rate,"+
            "ParentService=@ParentService,GrandParentService=@GrandParentService "+
            "where ServiceId = @ServiceId;" +
             "select ServiceId,GrandParentService,ParentService,ServiceName,Rate from Service";
            cmd.Parameters.Add("@ServiceName", SqlDbType.VarChar).Value = ServiceName;
            cmd.Parameters.Add("@Rate", SqlDbType.Decimal).Value = Rate;
            cmd.Parameters.Add("@ParentService", SqlDbType.VarChar).Value = ParentService;
            cmd.Parameters.Add("@GrandParentService", SqlDbType.VarChar).Value = GrandParentService;
           
            
            GridView1.EditIndex = -1;
            GridView1.DataSource = GetData(cmd);
            GridView1.DataBind();
        }



private DataTable GetData(SqlCommand cmd)
        {
            DataTable dt = new DataTable();
            SqlConnection con = new SqlConnection(strConnString);
            SqlDataAdapter sda = new SqlDataAdapter();
            cmd.CommandType = CommandType.Text;
            cmd.Connection = con;
            con.Open();
            sda.SelectCommand = cmd;
            sda.Fill(dt);                    //Error "Must declare the scalar variable "@ServiceId".
            return dt;
        }