You did not screw up your interview. Your interviewer messed up (assuming your account is accurate). This person should not be interviewing.
Every year we get stories like this, and I encourage applicants to alert Brown about these alums. Applicants are afraid to do this, thinking that it is going to hurt them with admissions – no matter how much I assure students that making a report will not hurt them. So, if your interview was as bad as you say it was – call Brown. I’d call Alumni Relations. Report this person.
If you do nothing … whatever this person writes up about you won’t affect your admission.