How to draw UI to the edge of the screen
By default, applications will have borders placed at the edges of the viewport to account for the TV-safe area (for more information, see Designing for Xbox and TV).
We recommend turning this off and drawing to the edge of the screen. You can draw to the edge of the screen by adding the following code when your application starts:
Windows.UI.ViewManagement.ApplicationView.GetForCurrentView().SetDesiredBoundsMode(Windows.UI.ViewManagement.ApplicationViewBoundsMode.UseCoreWindow);
Note
C++/DirectX applications do not have to worry about this. The system will always render your application to the edge of the screen.