SOLVED Different width main content div dependent on sidebar

I'm trying to achieve something in my template and hope you can help!

Within my custom mainbody.php, I'm trying to load different widths of the main body dependent on if a module is loaded to the sidebar:



But this completely fails and does not display anything.

What am I doing wrong?

Thanks

SOLUTION
My code above is wrong use:



This will then make the t3-content area full width when no sidebar module is loaded.

Hope that helps