No need….I can see it clearly in Web Inspector/Developer Tools
As I said, I know very little about WP and the themes/sub-themes.
Without taking the menu OUT of the wrapper that is keeping everything centred there is little we can do.
What you do in effect is something like this. http://codepen.io/Paulie-D/pen/oGKtA
Your main blocks are all 100% wide. If you want to limit the width you add an inner wrapping element (in the example I gave it a class of…oddly enough…”inner” and set the width you want on that.
Not sure WP &/or your theme will let you do that….