It seems that your theme's sidebar is not wide enough:
http://i.wpne.ws/Pmgj
That sidebar is wrapped in a div container with the . twocol class, which makes me think that your theme might be a 3-column theme, with 2 right sidebars. Is that possible?
Could you check your theme options? You might be able to change the number of columns from 3 to 2 there.
Otherwise, I would suggest that you edit the theme's sidebar.php to remove the .twocol div.
I hope this helps.