420x120 is the size we use for all the other sides. In this case, you need to crop the image a hair to get it to be the right size. What program did you use to create this image?
Photobucket only allows for resizing but is limited on editing. I would suggest downloading GIMP and do some youtube tutorials to help get you started. The problem is youre trying to get an image to fit a size, instead of making the image work. Let me know if you need any help, but GIMP is a good way to start.