Somebody forgot to put UI anchors to properly fit screen =P But I have zero complains since my SFX can kill someone's ears if they'll be not carefull enough...
Jokes aside - this is nice game with interesting gameplay! Great job!
The background is actually not supposed to have anchors, it's a parallaxing set of sprites that's used in every scene. The main menu just doesn't have a camera, so it defaults to the top-right being (0, 0) and the sprites are centered with the center at (0, 0).
Yeah, I talked about start menu. If scene have no camera, it must be defaulted to the viewport, so if you anchor that menu's background to the "full rect" it must do the trick. But I may be wrong. Sorry for bothering you =)