I think you are being too hard on yourself (as we know, it's part of the whole ball of wax of CPTSD). This situation has been brewing for a while, like a storm coming, and, while you knew how you wanted to handle the situation, you can't hold yourself responsible for someone else throwing a curve ball. Groups of people are hard to deal with in most circumstances, because everyone has different ideas, different agendas, and they bring their own personalities and baggage into it. Add in the tension of being assigned to a group with a lot riding on it (your grade), and it's understandable.

You see, the thing is, none of us here think anything like "oh, that horrible, stupid Jane, she blew it". Only you are feeling that, from an outsider's perspective, you were being human, doing the best you could under the circumstances, and being too hard on yourself.