Agreed with the above, it's a good thing she let you know, and I would try not to take it personally. It doesn't sound like the supervisor is saying she doubts your competency as a future psychologist, or had major issues with your understanding of crucial concepts; she's saying she noticed there was a lot going on when you worked with her, and it impacted your performance. It happens. You've seemingly identified some of the key problem areas so that you can address them going forward (e.g., by not over-extending yourself). You've made the best of it and have done what you can do.