1994 Corolla stereo install

I am trying to install an aftermarket stereo on my 94 Corolla. Wiring is fine (I tested it) but it doesn't seem to fit correctly. The face of the stereo doesn't stick out far enough out to be able to attach the trim piece that came with the stereo. There is no gap above or below the face of the stereo but there's 3/16" on either side. Am I missing something or do I need to buy a different stereo because only certain ones fit?