I have not tested your screen-size. But with some monkeying you may well be able to fill screen on this game. Have you tried:
1. windowed (low chance)
2. High chance: FWS with 3 FAKE VERTICAL monitors (2 short fake screens on top & bottom of a fake center screen of 16:9 resolution).
A. Go to FWS menu Settings, Configuration, Display Detection. Checkmark Enable Detection Override
B. Enter Width & Height (your real fullscreen), HUD W&H (your fake 16:9 center's size), HUDX (zero), HUDY (the height of your top-fake-screen).
C. Horizontal Display Count = 1, Vertical Display Count = 3.
D. Save changes.
E. If uncertain of the math, tell me your resolution...
3. High chance: Failing #2, try #1 & #2 together.
Hints in link below. But it's for manual PLP, so you must fake-out FWS bit different (vertically instead of horizontally).
http://www.wsgf.org/blog/imusrt/2015/10/23/sonic-all-stars-racing-transformed-manual-plp-instructions-2013