How can I change the width of the main column?

I installed the Sundance theme, but I increased the header width to 1150px and the sidebar width to 250px. These changes worked just fine.

However I cannot get the main column to cooperate. I want it to be 800 px wide and be lined up with the left side of the header. There is some sort of white padding on the left side of the column that won’t allow this, though – they made space for the gravatar to show up there, but I have turned it off.

Right now, if I increase the width of the main column, it simply overlaps the right sidebar. So I would like to know how to move the whole column over to the left (while leaving everything else the same).

Thank you,
-Maria @ http://www.trinemarie.com/