A good technique for patching holes -- anything from a big hole in a wall, to a small hole in
fiberglass -- is to cut a strip of hard material (plastic, wood, etc.) that is narrow enough to fit in the hole, but wider than the hole. Drill a very small hole in the middle of the strip, put a thin piece of line (I like fishing line) through the hole, and tied a big knot on the inner side of the strip.
Then you put the strip into the hole, position the strip behind the hole, and then push your JB or expoxy, or plaster if it is a hole in your wall at home, into the hole and against the strip. Let the material push in behind and along the strip.
That makes an area of the material expand on either side of the hole, so it will not be able to be pulled ouit once dry or cured. Smooth out the outer surface.
It would be a good idea to make the outside of the hole slightly countersunk, so that when the filler material cures the plug cannot move in or out of the hole.
Once cured, pull trim the line even with the wall with a razor blade. Then you will have a perfect and very strong patch.
Hope this helps............