What do you mean with "messed up"?
You've changed the top image - that's OK, but you did not change the border pictures...
./templates/default/images/header_top.gif
./templates/default/images/header_right.gif
./templates/default/images/header_left.gif
You have two options:
1) to edit these images
2) to delete change the template so that it won't need these images and shows up only the header_logo...