So it is January 17 and I got an email January 4 from Northwestern to sign up for an interview by January 8. I just saw this email today. I am extremely interested in Northwestern, and I do not know what to do. I already emailed the admissions office. I just want to know if anybody else has been in similar situations? Do you think my unresponsiveness will hurt my application?
Just a personal opinion. I do not believe it will dramatically affect the status of your application.
Yes. You should send a polite email to the admission office. If I were you, I would have called the office and politely explained and apologized the mistake. The reason in this case that a call is better than email is to show that you are not afraid of speaking to strangers, which is one of the main purposes of in-person interview. After that, I do not believe your chance of being admitted will be affected at all by this accident. A well-performed PR resolution is much better than any ordinary interview.
Turn the accident to be an opportunity. Good luck!