I am sure he will LOVE the school, give him 2 weeks and he will love it...
I know that feeling.. My son is a only child I got, and always will be. And I put him in school in August and it just broke my heart and I cried and cried all day even at work too.
Two weeks later, he LOVE it!! He love the teacher Miss Eva, and he even got his first girlfriend Gabriella (Gabby), and he made a lot of friends and learning a lot of things. This week, he and his class are learning the numbers, like phone number, 9-1-1, and so on. Last week, they learned colors and shapes. It's really amazing. I was looking at him, and said, GOSH, he is 3 years old and he know everything.
I know I know the feeling when I drop him off, it break my heart, but after couple days, I felt better, and the school make him happy, he is happy with his teacher and I am happy.
I am sure Sherry, your kid will be okay and I know it's not fair to let the kids grow up fast. I wish mine stay small.