I took a list into the confessional with about 8-10 sins listed. Halfway through I hesitated because it was somewhat dark in the room and I had trouble reading it. The priest abruptly interrupted with, “Let’s just consider it a general confession. All your sins are forgiven.” He then recited the prayer of absolution. The problem was that I had listed the sins from the least to what I thought were the worst and I was so rattled that I forgot what the entire pennance was and so did not complete it. Do I need to make another confession? I have received Communion since and worry that I have committed sacrilege by doing so.
If a mortal sin was omitted, go talk to the priest. Otherwise, it is wiped away and you are not at fault, since you intentionally omitted nothing. Actually, if you omitted a mortal sin, but through no reservation of your own, but because you were cut off for reasons having nothing to do with you, it could be argued that you did what you could and that is wiped away, too, since the priest clearly knew you had more to say and intentionally absolved you of everything without a full confession. If you felt you had no choice but to go along, then that is on him, not on you. Still, we’re not here to find fault with your confessor. I would explain the situation and confess it, anyway. If at all possible, give this feedback to the actual priest you confessed to the first time. That will be good feedback for him to get.
If you forgot the exact penance, you can hardly ask the priest to repeat what he said, but do your best to do something that requires exertion at least what you think was required.
The next time the priest interrupts or hurries you, do hurry up, but also remember that it is your responsibility to make sure there is nothing mortal held back and that you understand the penance before you leave. Don’t beat yourself up, though. You did not feel free to question his directions or to do other than what he told you the first time and you can’t have a do-over. Fix what you can, confess what you ought, and let God forgive the rest. Now that you know better, you’ll do better.
PS Put the stuff you absolutely don’t want left out, even if “only venial”, at the beginning. I have found it goes quicker to confess worst-to-least, and it is less likely that the things I struggle with the most will be left out or will be given “short shrift” in the advice department.