Need header image to be centered

I really need some help.

I’m using inkblot along with webcomic. For some reason by header won’t extend across the top of the page. I’ve tried both making the headers larger than the suggested 960×240 and smaller than that. Nothing changed.

I either need to know how to make the header extend across the page or be centered. Right now it is “left aligned” from the looks of it, and looks terrible. Any help would be greatly appreciated.

http://www.lesbionixwebcomic.com/