TwentyEleven Custom Page Template – Post width

Hi Guys,

I just would like to start off by telling you that I am new to WordPress and I am helping a friend create a website to help promote him (He is a DJ).

I created a custom page template using a tutorial found here which displays posts with certain category tags.

Then, I added a sidebar to the page template using a tutorial found here.
My page now looks like this: http://www.datdurty.com/mixes/

As you can see, the width of the posts on this page seem to be narrower than they should be. Also, now my other pages without sidebars are too narrow as well example.

I think it might have something to do with this code I added to my child theme’s style.css to have the sidebar display beside my posts on that page. `.singular #content{
margin: 0 0 0 7.6%;
width: 58.4%;
float:left;
}`

How can I make it so that the width of both these pages return to normal and still have my custom sidebar?