Setting Page / site width

I am new to Atahualpa. (using Atahualpa 3.6.4) setting up my first site but cant seem to find where I set the page or site width.

using "The Layout WIDTH and type (FLUID or FIXED) %:: (tried % or px) It just seems to push the site to the right, not reduce it.
Tried on opera & FF. - Consistent results on both.

By this response its seem that this is not even the correct setting, but i cannot find anything remotely relevant on the on theme or on the forum so so sorry for asking something which I would of expected is obvious.