My bubble, it is burst

When we enrolled DS1 in preschool this year, I was nervous. Not nervous in that "oh, my baby boy is off to school, will he do well?" kind of way, but more in a "will he behave and not get himself kicked out?" kind of way. The first few weeks were tough. He wandered away during the field trip, he tried to go out the backdoor of the classroom onto the playground an inappropriate times. We sat him down, discussed following directions and staying on routine. There were a few behavior notes, telling us that he'd bitten someone while sitting at the computer. We dealt with that, tried to get him to understand that we can lash out and hurt each other. But things seemed better. He would come home with stories of the fun things he'd done in school, not the times he got scolded. We would pick him up at the end of the day, and the teachers would tell us he'd had a good day. He looked forward to going to school each day, even asking me on weekends why he had to stay home. My phone rang today. "This is Laura, the Director at [$200+ a week preschool.] It's not an emergency, [DS1] is fine, but I need to find some time to sit down with you or your husband to talk about him." It seems as though he's backslid a bit this week. He bit somebody. He tried to punch. He headbutted a teacher (although the director said that it was not on purpose.) I almost started crying on the spot. "I thought he was improving," I said. "He's been doing well lately, hasn't he?" "He's a smart boy," she said, "but he does sometimes lash out. It would just be better if we sat down and talked about it. Every child is different, but at four he has enough words that he should be able to express himself without being so physical. Just let me know when you would be able to come in, and I'll make myself available." I called DH, and we found a time tomorrow that we can both be there for. I called Laura back to let her know, and she said she didn't want me to worry about the meeting. My four year old is biting, punching and headbutting. It's not even Halloween and I'm afraid he's broken the rules so much that he's going to be expelled. What, me worry?