First, socialization can be done without puppy classes. Puppies present the LARGEST risk to him for disease. Introducing him to dogs and people you know, particularly dogs that have completed their vaccinations and are older, it almost totally safe after the initial shots.
Second, Petsmart isn't somewhere I would take ANY puppy. They bring in rescues and shelter dogs, they do not require proof of vaccinations, and they let people come in. We had an outbreak of parvo some are sure they got there as it was the ONLY common place.
Third, Petsmart notoriously has sketchy trainers. Some areas are good, most not so much. I just filed a complaint at our local one after observing TWO of their trainers pop and jerk puppies.
That said, anywhere BUT petsmart, that requires proof of vaccinations started, should be safe and fun. This link has a lot of info, including the assoc pet trainers link at bottom. See what is available.
MOST people, really, are able to train their pups on their own. (NOTE… pets. If you plan to show or obedience or compete, you need pros! ) Socialization doesn't have to be in a class. But socialization is utterly totally important. Having gotten a dog (Arwen) who basically had NONE til almost 14 wks old, it is a hard learning curve to overcome. That said, I have also done rehab on feral dogs. You can over come it. But why make life harder. Just don't buy into the only way to socialize is puppy training classes. You are already doing a good job. In fact, I suggest that socializing with HUMANS of all sorts, shapes, sizes, colors and ages is even more important than with other dogs.
http://www.ehow.com/info_7889981_tips-puppy-behavior-training.html