I've found it incredibly helpful to be able to tell my therapist what I feel are my deepest most shameful horrible secrets, things I fear will make him recoil in disgust and tell me what a bad horrible person I am... and have him react compassionately and completely without judgment. One of my most shameful secrets surprised him, not because he thought it was horrible, but because he was surprised I would consider it horrible and shameful. His response was a much more tactful version of "wait, really? That's it?"

I can't speak for your therapist, but I think if you bring it up you might have a similar experience.
Speaking completely personally, my reaction to reading your "admission" of the event was "wait, that's it?" I can't imagine a therapist holding it against you, let alone believing you to be a horrible person for that. As others have said, it sounds like normal teenager stuff. You listened to your friend when she expressed her wishes, and it sounds like you learned from the experience.

I think a T would be a lot more interested in why you're judging yourself so harshly for something like this. I don't think anyone else would condemn you for this. It's the kind of thing that makes for an awkward memory that you cringe at, not the kind of thing that warrants pervasive shame and guilt years later.
I really hope you talk to your T about it and she's able to help you with this.