Quick Question About the Page Bar...

Hey -

Just a quick question about getting the page bar to look right. I'm currently converting my site to the Atahualpa theme, and my test site is here:

http://www.3rdrate.com/blog

The current working site using an old theme is here, for comparison:

http://www.scoutingny.com

As you can see, I have a black nav bar going underneath the header image...but it stops at the last button, rather than having a rectangle of black to cover up the unused space. How can I get it to extend to the other side of the page without adding additional buttons?

Thanks!
Nick