Or was it that I’d never believed in myself to begin with?

First, "commentment" is not a word in English--not that i've ever seen. Comments works just fine in your sentence.

The author states that her teachers didn't know her, that they had never takent the time to find out who she was, to explain the incident in which she had been humiliated. Then, she offers an alternative explanation, which is why the last sentence begins with "or"--which is not that her teachers didn't know her, but rather that she lacked self-confidence, that she had never believed in herself.