I always have problems with the UI on different screen sizes. Could it be that in full screen you are still missing the bar on the bottom that shows which keys are available to you? Have you tried pressing "X"?
Hmm, I see the bar, but they doesn't do anything. I dont' know, arrows should move me left and right? If yes, they don't :/
Opera, Windows 10
I don't know what to advise you. The game is super short. I made a let's play video and it is 3 minutes long :)