When I opened the game the only screen option on the configuration menu was "100 x 1179649 (rotated)". This is, believe it or not, not the correct size for my display.
Opening the game resulted in exactly what was promised. This also meant the actual game size was too small to see or do anything.

It was fixed by restarting the game and I've never seen it happen before. I'm curious if anyone knows the cause. This was on a laptop with no external displays connected.