are the "bumps" not wide enough to fit snugly in the holes? Why not build them up by wrapping the bumps with duct tape a couple of times. The tape should be out of view and the cover should work as intended.

Old thread but others may have the same problem. I used small colorless ties through the holes at the sides for the "bumps" and small holes in the cover. The only downside is that one must cut the ties to open the cover- an event that does not occur often.