This is caused by the social media icons you have on the footer. It has an inline style of 600px width, even on mobile. What widget are you using for this? Is it responsive?
Since you’re placing it on a module, you could try creating 2 versions of it. One for large devices, where the icons are bigger, then the other for mobile devices, smaller icons. You can then configure it so the first one only appears on large devices under Advanced > Responsive layout.