[Twenty Thirteen] White space on right side on mobile

Hi all,

Having a bit of a problem with a site I’ve put together: http://www.pumpkinbeth.com.

It all looks fine, until we browse on mobile, and then there’s a white border down the right side.

Tried a couple of fixes, e.g., as indicated here:

https://wordpress.org/support/topic/twenty-thirteen-margin-on-mobile-devices?replies=21
https://wordpress.org/support/topic/twenty-thirteen-white-space-on-mobile-theme?replies=5

But adding this in my CSS:

.site-info
.site-footer .widget-area {
width: auto;
}

but to no avail. Tried removing widgets, changing the footer, and various other stuff, but no joy. Starting to tear my hair out!

Could you advise what the problem might be? And also give me an indication of the Chrome tools I should use to debug this myself in future? 🙂
Thanks!