Center the menu when hamburger opens

Hello,
On my dev site - http://www.keepsafestorage.co.uk/
I have the burger set to show on desktop and mobile - This is what I want.
When I click the burger the nav menu opens but all the menu is on the left. How do I center this? This is not too much of an issue on a mobile but on a desktop its a long way to mouse move to select the pages I want. Have I missed a setting?

The Navigation Alignment does not seem to change anything -

Thanks.