Nervous about Preschool

My son (3.5 yo) starts full time preschool in 2 weeks and I'm very nervous. He's gone to a home daycare (4 days a week 8am-4pm) with 3 other kids for nearly 3 years.

This preschool has 20 kids in a class and 2 teachers- this seems like a lot of kids to me but I'm hopeful he will do well. We've only ever heard wonderful things about the school. Other kids from his daycare have moved onto this preschool too and have done well.

I'm just looking to see if any other moms have had good experiences with full time preschool at age 3- I work full time so we need a full time program for him but for some reason M-F 8:00-3:00 seems very rigid for a 3 year old. Either way I know it's time for him to move on from his home daycare because he's maxed out from what she can offer him there educationally.