My son never liked the circle stuff during the short time he was in preschool. I didn't blame him- I mean, I would be totally weirded out if a group of people started singing directly to me, lol! Why should we expect kids to feel differently?
Quite honestly, I feel all the sing-songy talk and structured social stuff (a.k.a. "circle time") you see in most preschools is pretty unnatural and not like people interact in real life at all. That's one thing I appreciate about Montessori schools- there's more of a natural and respectful atmosphere, and the children are able to structure their own time and choose what is meaningful for them. Homeschooling, which is what we've chosen, also provides that.
Also, three is so young! If he feels supported by you and is allowed to stretch his independence on his own schedule, he will be so much more secure in the long run (in social situations, and, more importantly, in his own skin :).