Changing the width of a section

Hi, I’m trying to create a blog: http://blog.cavernproductions.com/

Based on the Equilibrium theme. I’ve edited it a bit to put the sidebar at the top but whenever I try to add content in the sidebar it pushes the Latest Posts down. I was told this is because the width of the Latest Posts goes all the way across the screen. Does anyone know where I can edit that so it only extends to the sidebar?

Thanks