You have a div, 'maincontent' which is 953px wide (full width). This contains just your left column.
Below that (not contained inside your 'maincontent' div), is a 'container' div - which in turn contains your 'carteditarea' div.
I'm not sure that you need the 'container' div, but the 'carteditarea' div should moved to be inside the 'maincontent' div. You could select it, and cut and paste it into the maincontent div.