Hiding content regions in custom theme using Panels 2

Hi,

I'm working on redoing the main website for the school I go at with around 1000 pupils.

I've made a custom theme using Artisteer (http://www.artisteer.com/), and am now using Panels 2 to make custom views.
What I'm trying to do is have the content in the panel I made to stretch the entire width of my theme's page by disabling the left and right sidebar content regions.

I have tried:
a) hiding all blocks on the page;
b) selecting the supposed "Disable Drupal blocks/regions" checkbox under Variants » Panel » General in Panels 2.

First I hid all blocks. This causes the panel's content to move up to the left, thus "covering" the left sidebar region. However, the content keeps it's original width of the "center" content region. I later found out about option b, but this made no difference. I've read elsewhere that this could be down to the fact that I'm using a custom theme.

Could someone help me make this work? I'm able and willing to make changes to the code.

An example can be found at
*snip*

Thanks in advance!