[SOLVED] Added header images cut off on both sides

I've gotten as far as uploading my new header images. They are in the same folder as the defaults, which I don't want to delete until I'm sure the new ones work like I want them to.

I made the new images 1300x160. But when they display, they only go over the center section, and not the left and right sidebars, like the default images do. This leaves white space on both sides of the image, above the sidebars, and I don't like the looks of this.

Please advise, what can I do to fix this?

I've tried different image dimensions, or none, but none of these ideas has produced the desired results.

Thanks!