I looked it up and a 90 is about a 3.5 gpa, which is low for Penn (but people have still gotten in with similar gpas, so don't worry too much!) If you're not applying early, I would try to bring your grades up a little. Did your letters of rec talk about grade deflation at your school?
You should also work on your essays a lot, since those play a huge role in the admissions decision. Show that you're really passionate and unique and would contribute to the diversity at Penn. I think you should talk about your passion for writing, because your novels will really help you stand out.
Overall, I think Penn's a reach because of your gpa, but you could definitely get in because your extracurriculars are really strong and your writing skills mean you can write amazing essays.