You don't want to react too strongly to a first day. Howver, it is important to underscore that he is to do what the teacher says. Hopefully the teacher will set a firm limit on this and be resolute in his/her expectation that your son is to follow directions. For now, setting the limit, supporting the authority of the school, is all you have to do. If your son does not comply soon, some disciplinary measure might be needed, but give it a few days.
This sounds to me like a case of a young child having anxiety being in school for what could be his first time. I think the best thing you can do at this point is to continue to stay in touch with his teacher, and also prepare your son for school the night before as best you can: including ensuring he has a good breakfast, going to bed early, re-assuring him that school is fun, and letting him know that these behaviors will not be tolerated.
If they continue past the first week or two, then it is time to start looking at a behavioral management plan that yourself and his teacher can put into place.