wordpress columns theme doesn't match

I have a problem with my website:

www.iranautomation.com

the problem is with the size columns, main and sidebar. The whole area is 970px, main-content is 660px and sidebar is 300px with 10px blank area between two columns but it is not like that and it goes to 988px and disrupt my columns view. I try everything but nothing is happening. So anyone can help me to fix this problem??? I really appreciate your help

www.iranautomation.com

Thanks for your support ;-)