Resolution Problems for Visitors

I recently extended my site structure, from 960 px to 1300 px.All good until I noticed that it doesn’t auto optimize anymore to all resolutions for viewers.I’ve been looking for a script that could help me detect and update viewer’s browser resolution but I have no clue how to get this done.My resolution is 1680 x 1050 and it still appears in the middle where it’s supposed , but for those who have lower resolutions it’s needed to scroll over to see the full width.

A link to my site here
Really need to resolve this somehow,thank you.