problem Dynamically freeze ASP.Net Gridview header using JavaScript

http://www.aspsnippets.com/Articles/Dynamically-freeze-ASP.Net-Gridview-header-using-JavaScript.aspx

It's work,but

My table is not aligned.

The data field for the group name does not align with its title filed.

Can you tell me where I did wrong?

Thanks.

 $(document).ready(function()
             {
                $('#<%=gvtest.ClientID %>').Scrollable({
                    ScrollHeight: 84
                });

             }); 

<asp:GridView ID="gvtest" runat="server" AllowSorting="True" AutoGenerateColumns="False"
                                                    Width="100%" OnRowDataBound="gvRight_RowDataBound" UseAccessibleHeader="False"
                                                    CssClass="GridViewStyle">
                                                   
                                                    <Columns>
                                                        <asp:TemplateField>
                                                            <ItemTemplate>
                                                                <asp:CheckBox ID="ckbFlag" runat="server" />
                                                            </ItemTemplate>
                                                            <HeaderStyle Wrap="False" Width="10px" />
                                                            <HeaderTemplate>
                                                                <input id="ckbAll" runat="server" name="ckbAll" "
                                                                    type="checkbox" /></HeaderTemplate>
                                                        </asp:TemplateField>
                                                        <asp:BoundField   DataField="GroupName" HeaderText="GroupName"
                                                            ReadOnly="True" >
                                                            <ItemStyle Wrap="False"  />
                                                            <HeaderStyle Wrap="False"  />
                                                        </asp:BoundField>
                                                    
                                                    </Columns>
                                                     <HeaderStyle CssClass="GridHeader" />
                                                    <EditRowStyle CssClass="GridEditItem" />
                                                    <AlternatingRowStyle CssClass="GridAlterItem" />
                                                    <RowStyle CssClass="GridItem" />
                                                    <SelectedRowStyle CssClass="SelectItem" />
                                                </asp:GridView>