Publisher web pages are left justified by default, and there is no built in
way of centering the page or "removing" the white space.

Reference: Understanding background padding in a Publisher web (aka white
space):
http://msmvps.com/blogs/dbartosik/archive/2006/01/07/80563.aspx

If you want to center your pages, you can edit the html code of the pages
each time you update them. The specific method of doing that depends on the
version of Publisher you are using.

DavidF