Correct screen size problem
 

I have 2 forums one 3.7, one 3.8 if it makes a difference. I set them up on my widescreen computer and they stretch all the way across the screen. When I go to one of my older computers that is not wide screen the header is getting cut off on the right. (other people are saying they are getting cut off as well)

I visit several other forums (not mine) and on theirs it makes do difference what computer I am using I can see the entire forum.

What am I doing wrong with mine?