I'm having the same issue. On any page that is a gallery it looks fine, however on my "about" page, which is just and image and a text box, I can't figure out how to center this but keep my logo and navigation split like the OP's example. I was hoping to resolve w/o any added code. I am also using the Wexley template.
If I center the Site Alignment it stacks my logo and navigation which I don't like.