When we went to puppy pre-school with Phoebe she was in a class of about seven as she and a little maltese were just about the same as your baby.
It was wonderful to watch them (Pheebs and the little malt) gain confidence as the weeks went by. By the end of it they were in the middle of all the puppy mischief - chasing, being chased and giving their funny little puppy yaps and running around. You would not have believed that they were the same puppies.
Sounds like you are doing everything right by reassuring your puppy and putting him back down again. Baby steps. Persevere. I'm sure he'll be fine. It's worth it in the end. You'll end up with a happy, friendly, well socialised puppy.
Keep us posted and let us know how you go next week.
Sandra