Game renders on lower resolution than it's supposed to

Hi everyone,

I'm working on this game with multiple scenes and I did something wrong while I was creating a settings window where the player could change game resolution and graphics. Now the game is running on fullscreen on incredibly low graphics (might be the resolution, since when I change the fullscreen mode in-game it becomes a really small window). The game looks fine in the editor, I tried configuring and resetting player settings, but it didn't help. What is more, the game has over 30 scenes and I was working only on one of them, but this messed up the whole project.

Here's how the game looks in Game View: https://gyazo.com/f8b2750674346ba8bcfd0df881311e37

Here's how the game looks when I build it: https://gyazo.com/f287d9ed6c68810b82f767f0ab78425e

I feel like this is a stupid and simple problem, but I've already spent too many hours on this with no significant progress, so I really need help.