Left Align Boxed Element

I have a full width element with an inner section. I’d like the inner section to be boxed and left-aligned. I want it boxed because I don’t want the second column to take up the full-width because my blog images are getting distorted. How can I left align the boxed inner-element? I don’t want to use the left margin trick just because it messes up the mobile version of the site with the blog post grid barely on the screen.

Any suggestions?