superdrive problem

I am having trouble getting my superdrive slot on the top case to line up with the actual slot after swapping out my old dented bottom case for a new one. When I try to eject a disc I have to use a flat thin object (in my case a pocket knife) to press down on the case slot to create enough space for the disc to eject enough for me to grab before it sucks it back in. Is there a trick to getting this lined up correctly?