Not sure why you can't walk him? While avoiding dog parks and other areas frequented by many dogs, we knew our boy needed some exercise, so we walked him around the streets of our neighborhood; two to three times a day, as the rule is 5 minutes of walking for every month in age.
Have you put him on the floor and laid on him to show him who the pack leader is? It is important he learn that ASAP
Our breeder recommended we socialize him every day, or as much as possible. When my wife went grocery shopping, I would sit out on the bench with him, and he was the hit. I had folks taking his picture, and even got asked out twice (LOL). We also took him into Home Depot, Lowes, Bed Bath & Beyond, and pet stores.
Once he had his shots, he met some other puppies who live locally, and we meet at least once a week at the park for them all to play.
While we didn't do puppy class because we were teaching him basics at home, he is now 6 months old and in obedience class.
Exercise, socialization, and training are the basic keys to having a great Lab.