Well, i mean, you can always just go to the registry and enable fullscreen 😊
go to HKCU\Software\HotPink and Annue\Tentacle Locker
FInd 'Screenmanager Fullscreen mode*'blah blah something, and the set the value to 1.
When you open the game again, it'll be in full screen!
(No fair altering your score tho 😋)