Your in luck kiddo. I just modified that default Ning theme your using.
I started with it on a network I am designing. I had been making some heavy mods to it when I noticed after my last save that the entire network had shifted left.
What is happening?
Since you not utilizing that CSS, it will have to be removed. If you like, I can join your network and you can give me access as an admin to the appearance area of your site and I will remove the code that is forcing your banner to the left.