Hey Maria,
First author, wow! That's incredible! In my experience, thus far, interviewing with UCI; I learned that your BCPM, LOR, an personal statements are weighed heavily. In your case, the first author publication is not going to hurt you if you already submitted your application. If you feel that you should email them, and let them know (maybe to clear up your conscious and nervousness), then shoot for it girl. Point being is that from my application, I had a lot of research experience, but none with first authorship only credited in acknowledgements etc. I believe since they are judging you on your grades, essay, and LOR and extracurricular activities, you should not worry too much if you didnt include it in your app in time. If granted an interview, make sure you emphasize your first authorship and research experience in the portion of questions, where they ask you: do you have any questions or comments. Just elaborate and make yourself look like a stellar person you are, and you will be fine. Hope that helps.