In order to change the left margin, you'll have to modify the Metro theme RadTabControl ControlTemplate. The ScrollViewerElement of the template has a predefined Margin of (2 4 2 0) so you can just change it to remove the left margin value.
I attached a sample solution demonstrating this approach, so please have a look at it and let me know if it works for you.
Is this a style I can override? or do I need to adjust it in the existing implicit template ?
answered on 02 Oct 2012, 11:52 AM
The style you need to edit is the default Metro style of the RadTabControl. If your application is using implicit styles, then you can find the RadTabControl style in the Telerik.Windows.Controls.Navigation.xaml ResourceDictionary and modify it to remove the left Margin of the ScrollViewerElement.