I am also a newb in css, but I imagine your image is bigger than the header space reserved for it, and it is not automatically re-scaling. So, you could either:
*resize image in photoshop
*enlarge header image space – someone will tell you where to do that since I can’t…
anyway, it seems the image has not the same ratio than the header space, so you will probably have to resize it in photoshop an cut some borders.
hope this helps!
