Pre-Pre-School

So my son gets babysat by my grandmother while we’re at work. She’s nannied kids for ever and is amazing. However I noticed he wasn’t getting socialized as much as the kids at day care do and because of this is pretty nervous around others. I started him in a co-op pre school twice a week for two hours at a time. They do little things like story time, and play time and whatnot. It’s not really a pre school as much as a place to get socialized. Well he HATED it today. Cried and cried, threw a fit, the whole 9 yards... I feel bad and I don’t want him to feel stressed while there but at the same time I know he needs it. What do I do? Any advice helps. Should he stick it out? Will he get used to it? My husband thinks it’s better him throw fits now than when he goes to actual pre school.... but us mamas know we don’t like it when are kids are upset....