Im having trouble making a full background billboard site(The size is 1600 x 600 the billboard) which has all the pages on one page for my portfolio, the problem i am having is how do i male it so it is always centered because when i make i and check the layout in a browser it is too big and at the bottom and the right hand side slide appear to see the other part of the site i wish to make it centered like this:

but i am having this problem on my site:

pls can some one help me i would be grateful thank you all