Background is stuck on my game preview please help

Hey i know this is probably a very simple thing to fix but im very new at this and ive no idea why the backgorund is appearing on the right hand side there (circled in red). Ive check if ive accidently put any items there or anything and there arent any. im at a bit of a loss sorry guys, any chance someone could help me please?

I believe you have your “Game Properties” set to change for window height, not width. Here is where to go and check:

Change it to no change or change to width and see if that helps.

Thank you so much for your help!