declared Blog as posts page and content area width increased

Greetings —

I’m using twenty twelve (gandrcustomcabs.com), sometime between last night and today the content area (which looks like a white piece of paper) of each page changed. Last night I declared the posts page to “blog” from Settings – Reading menu.

Typically the content area width is slightly smaller than the nav bar on the left and right sides. Did I inadvertently make changes to the content area of entire site?

Is there a way to review changes to the template (I know this is possible with posts)?

Just to give you a big picture overview, I was setting up an RSS feed to an email campaign (which is why I declared the posts page as “blog). Other recent changes to the site included adding a “blog” link to the top navigation bar, and made minor/styling changes to existing blog posts.

thanks,
Stacie