During Chapter 3, does Kambili fit in at school?

I see no major reference to Kambili and her schooling in this chapter. Please check your question.

Like Jill said, chapter 3 is not about Kambili's schooling. I think you're referring to Chapter 4. In which case, no she does not fit in. Because of her wealth and peculiar behaviour (she is very quiet in class and when school ends she runs home) they consider her a "backyard snob". It seems like only one person in her class really associates with her, Ezinne. We can assume she acts this way because she was raised in a very strict fundemantalist household, before she gets to go to Nsukka she is basically taught what to say and how to act and deviating from that can result in severe punishment from Papa.