There are three screws that are longer than the rest. Maybe you are trying to put them in the wrong spots?
There is a picture at this link...you might have to refresh if it doesn't show the first time.
http://support.apple.com/kb/ht1270#link1
Used that chart on my iPad... I'll leave it for now. If I continue I'll need new screws. I placed each screw back into the location they were removed. All the long screws are positioned fine.