Group not stretching when page does

So I am building a one-page mobile app. The Width of the page is 320 px to fit any phone, but I want the page to stretch in case the screen is bigger. My header and my footer are stretching without any problem, but all my other groups within the page are not. I made sure that the width is not fixed and there is no maximum neither. Any idea what the problem could be?
Thank you for your help!

Send some screenshots, fam. Or better yet, a link to your editor.

I guess you have some internal group with an errant checkbox for width rules.