i think the pet centre deserves to be reported anonymously to crime stoppers.
In the meantime I would not tell anyone about the possible "amstaff".
I'd also think about keeping the receipt, and if council does decide your dog is a "pitbull" you can use the receipt to get them or your consumer affairs or your police to get your money back for selling you something that is not legal for them to sell and "not fit for purpose" as a pet. "not fit for purpose" is a magic legal phrase to get shops to give you your money back for things that are sold as one thing and turn out to be another.
But puppy is adorable - very difficult to give up something like that. I know people who have kept blind or deaf or wobbly puppies because they or their children can't bear to give them up despite their problems.
Do all the right things by your dog as ChoppaChop said. Get it desexed, microchipped, registered with your local council, and join an obedience dog club. And never let it bite anyone. Will need practice. And like I said before, hitting puppy for biting not always effective deterrent - it's like punching back when someone tries to punch you, ie likely to escalate the "game" or fight.