accidentally called interviewer by first name.

i realized i had been a couple days late in returning a voicemail, and in a hasty rush i called my interviewer immediately and called her by her first name upon her picking up. she sounded offended and said “firstly that is ms. ____” and i apologized for that and not calling back quickly. she never said it was okay and i feel like an idiot. how badly might i have screwed myself for the whole interview before it has even happened?

Well, you apologized. If she doesn’t accept your apology, you have done all you can do.
I have heard interviews don’t count for much anyway.

Agree with above. You did as much as you can do. Honestly it’s not going to hurt you. Do you think admissions is going to say “well, the 17 year old who is probably nervous as hell, accidently called an interviewer by her first name - reject!” of course not.

Thanks guys!