I assume you don't want the screen to be distorted (keep aspect ratio).
You could, in full screen mode, try step-wise pan-scan using [+] & [-] of numeric keyboard.
([5] of numeric keybourd will undo pan-scan)
You could try movie-mode by depressing [M].
and you could try
(rightclick >) Options > Preferences > Video (> [General])
there check (select) the box "Cut top and bottom of video in full screen mode"
Is any of these options meeting your wishes?