How do I make pages stay within site layout in the infinite scroll view?

Strange thing: the infinite scroll archive only breaks the layout at browser resolutions over 600px. Below 600px in width, everything looks how it should.

Also, when I go into the customizer, everything looks good at any resolution, but once I exit the customizer, the pages are poking out of the layout once again (if my browser window is over 600px in width).

For some reason, image attachment pages behave the same, with page content sticking out on the right when my browser is at over 600 px in width. Here’s as example: https://bitsfair.com/bf-logo/

I changed the responsive width to 802 px, so now the exact same thing keeps happening, but with browser sizes over 802 px rather than 600. Should I just change the responsive width to something like 2000px to catch all monitor sizes? I’m worried this would break something.