XF 1.5 Random Background Space I Need to Get Rid Of

[aeriverse]

I wouldn't be here if I hadn't tried so many options, but what seems like one of the simplest issues to fix has stumped me. There's a horizontal scroll at the bottom of my theme, and whenever I scroll over to the right side there's a bunch of unexplained blank background space. I know, I know, you can just say "well why don't you just not scroll!", but this is visible for my users as well, and I'm frankly confused and frustrated as to why it's there in the first place. Does anyone here know how to remove it?

Spoiler: screenshots

normal layout (what it's supposed to look like, minus the horizontal scroll at the bottom):


what happens when you scroll over:


yes I know my theme is very unfinished