1 sidebar, left

Hello and congratulations for your theme.
Use the 3-column system with a total width of 1100px on the home page. The two sides are 250 px sidebar. When I go to a specific page that I’d like to go thema du two columns, a left sidebar and content only. The problem ‘that the content I rimande of 600px and does not expand also including the right sidebar so it should be 850 px wide instead of 600px rimanse. I understand that this depends on the general settings but how can I solve this problem? I tried to edit the template 3 column eliminating the sidebar right, but the content remains at 600. As work on the CSS? Thank you and congratulations.