Make my site 100% in width

When my website is viewed on larger screens, the site does not fit the whole page. My website is: http://atp.leontomlinson.com/prebeta/

If you go to it and zoom out on the browser, you can see that it doesn’t stretch with the page when you zoom out. I have tried using:

width: 100%

but Im not sure if I am using it right.

This is pretty urgent as it is for a client and due to give it them tomorrow.