Game Is Stuck on Demo Mode

[CasualPolarBear]

I bought Gunpoint during the last Steam holiday sale. I played the first few missions, but now I can't progress any further cause instead of the button that usually says "start game", it says "buy game". I know I own the game, because Steam won't let me buy the game for myself since it says I already own it. I've deleted it and re-downloaded twice already. Does anyone have any other suggestions on how to fix this situation?