You ruined it? You didn't ruin anything. You weren't sure if you were ready to have sex with her. And she didn't ask for consent.

It sounds like you were peer pressured into having sex in a context that you weren't wanting (with an audience) and so you felt you were ruining things. You were awkward BECAUSE YOU WEREN'T COMFORTABLE. That's on her, and on the group, for not checking in or caring about how you felt emotionally about the whole thing. There was definitely lack of enthusiastic consent there. Arousal doesn't mean consent. Not saying no doesn't mean consent. Kissing doesn't mean consent.

Not saying your friend is a rapist but there was definitely something wrong happening there and it was NOT your fault. It was on THEM (Abby and the boys there) to communicate better with YOU. Not for you to magically change your feelings of discomfort into porn star enthusiasm for them.