Windowed game not centering

[BelGarion]

So I have a game that plays in windowed mode only. I went into Settings -> General and made sure Source Alignment Snapping is checked as is Snap Sources to Horizontal and Vertical center. I wiggle the preview about but it isn't snapping to the center. As I plan on adding a border around the window (to pad it up to 1920x1080 without stretching or making it look any worse) this'll be a problem. How do I center it?

 

[BelGarion]

Using Windows Capture . Well... Windows Capture on top and Game Capture under it set to Capture Foreground Window with Hotkey hot keyed to Skyrim LE. So it is windowed mode.

 

[koala]

In OBS, to do something with a source, right-click the source and find the operation you want to do in the context menu and its sub-menus. Centering a source is found in the "Transform" submenu.