Layout Dimension problem

Hey There,

I have been trying to figure it out with trial and error but failed to do so miserably so far.
I added a custom CSS for table header and i also saved some templates for copy/pasting from one layout to next.

While doing that somehow i modified the size of the main container. I change it to 100% and i play with pixel sizes but its not budging.
If there is any chance you can help me i would appreciate it. It affecting all the pages at the moment.

thank you