WELCOME!!
First thing is the 12Ga barrel is mighty thin and using a factory setup with only three screws is a recipe for problems. I have put some peeps on 12Ga guns, but the peeps weight and leverage it can put on the screws is infinitesimal in comparison to mounting a scope on one. If I was forced to do this, I would make my own mount using a universal rail and put in extra screws, I would open those holes up to allow #8 screws and then clean and epoxy that base to the barrel.
Good luck,
CW