How to set width of header widget

I've added a header widget to this site:

YourGameConnection

It goes across the whole site, but I want to shrink it so that the right side bar slides all the way up next to it. How can I set the width of the header widget?

Here is the code I tried already.

<?php bfa_widget_area('name=Header Widget&cells=1&align=1&width_1=900'); ?>

The width of the entire site is 1100 px. The width of the sidebar is 200 px.

Thanks.