Yes. You will have to prepare the surface like any other fiberglass repair, make sure it is dry and apply the material to make the repair. There are those who do this for a living that can replicate the finish of the original without having much of a different look. The problem is that there must be voids under the pan where the mortar didn't cover the base evenly. Did you mix up the mortar fairly loose, like the consistency of a thick milk shake? That allows you to build the mortar up fairly high, then slowly bring down the pan while the material oozes out the sides. This excess can then be banked/packed in around the open sides so that the product completely is surrounding the pan. Always put down plastic when putting mortar on a wood subfloor.