Hi Tom,
if you switch to the "standard" Moodle theme, does the page display more as you would wish? If yes, then you need to find out which css settings in the Gourmet theme are reducing the width of the containiner, and then override those.
There are a number of ways to override CSS in Moodle depending on your Moodle version. I believe Moodle has site setting to allow you to insert CSS via the Moodle interface, so that would be a good place to start.
regards
Gordon