Why not use Game Capture instead? Since you are playing in fullscreen I assume you don't have other elements you need to record, so Game Capture should work fine. I just tested it and it worked perfectly even if I start recording before launching the game and records through changing between fullscreen and windowed.
If you still have a problem with it being cut off you can try right-clicking the source and messing with the options for Position/Size, particularly you can try reset size or cropping and then fit to screen.
If you still have a problem with it being cut off you can try right-clicking the source and messing with the options for Position/Size, particularly you can try reset size or cropping and then fit to screen.