First off, it's not a good idea to use the classic template for customization. It will come back to haunt you big time.
You have "massaged" the layout quite a bit, but you can start by adding margin: auto; to the #pagebody call in the style.css.
Again, it's better to follow the Tutorials/FAQ for a custom template and keeping the general framework would have had a margin: auto; listing in the stylesheet.css.




