Game doesn't fit on my screen half the time

Literally 50% of the time, every other time I open it from Steam, the game doesn't fit the screen. It's massively oversized and only about the top left quarter of the loading screen is visible. All of the buttons are off the bottom of the screen. I guess hypothetically I could still click them, but it'd be random guessing and clicking to try and find them. After a quick alt + F4 to close, I reopen it and it's fine. It fits the screen normally and I can play.

Why does this happen and how do I make it stop?