Would it hurt if your puppy has had it's shots twice?

On a general basis your vet would only give one shot to your puppy. However, phone your vet who gave the last shot to your pup and ask about this. Perhaps the vet gave two different vaccines. If you bought the dog and it has had it shots already then there should be vet papers that came with the dog. If not let your vet know right away. You can phone them without any cost.