Twenty Seventeen theme not displaying full width on laptop

I usually work on my desktop and resize the window to see how other screen sizes display, so I was very surprised to see that on my laptop my website was not displaying full screen. There is about 20-30px of background on either side, no matter how I resize the window.

I can’t seem to find the css that would affect this. I assume it must be a media query of some sort?

The same problem does not appear on every laptop.

I took a screenshot but can’t seem to attach it (since it may be difficult to replicate). As I said, it doesn’t happen everywhere, just on my laptop (MacBook Pro, 12inch screen) and in both Safari and Chrome.

The page I need help with: [log in to see the link]