Had the same problem with a late 2012 Mac Mini who's grill would just not line up with the screw holes. I had read another comment on the ifixit instructions for swapping out the hdd suggesting a paperclip to hook through a hole in the grill, but I found that a paperclip was not stiff and sturdy enough as a lever. What did work for me was using one end of the Mac Mini logic board tool hooked into a hole in the grill, and gently working the grill up and in along the rim it was resting on. The grill moved right into place with an audible snap. Thanks Kevin!