The Twenty Eleven layout for posts on the home page and individual posts is different, here is an example from the demo for how they should look:
* http://twentyelevendemo.wordpress.com/
* http://twentyelevendemo.wordpress.com/2011/05/04/a-bowl-full-of-flowers/
Also see this link for more info about how the Twenty Eleven theme is designed to work:
http://theme.wordpress.com/themes/twentyeleven/
In your case, it looks like the following custom CSS you added is causing the formatting change for the single post layout:
#primary {
float: left;
margin:0;
width:700px
}
#content {
margin: 0 0 0 76px;
width:584px
}
#secondary {
float: right;
padding-left:30px;
margin-bottom:26px;
margin-right:76px;
width:188px;
border-left:1px solid #e2e2e2
}
If you wanted to apply those CSS rules just to your home page and get the single posts looking like the demo again, you can prefix the related custom CSS with ".home" to limit it to the home page like this:
.home #primary {
float: left;
margin:0;
width:700px
}
.home #content {
margin: 0 0 0 76px;
width:584px
}
.home #secondary {
float: right;
padding-left:30px;
margin-bottom:26px;
margin-right:76px;
width:188px;
border-left:1px solid #e2e2e2
}
P.S. Fantastic site! BYU theatre must be a blast. I'm a UofU grad. I only went to a few event at BYU, and I had a lot of fun. There's so much amazing talent there, it's crazy. :)