Hi!
Your stats are pretty solid! You have a good GPA and an ACT score that lands somewhere between the 50-75th percentile for USC applicants.
However, you should mention what you want to major in. That may significantly impact your chances of admission. If you are interested in cinema, USC will be extremely hard to get in to. Dornsife majors are generally a bit easier. I was accepted to USC for political science, which is in Dornsife. My stats were similar to yours (3.87 GPA, 33 ACT).
Now, after determining what you would like to major in (or after thinking about possible career paths that interest you), you should get involved in more extracurricular activities that are related to your fields of interest.
For example, I was interested in political science, so I wrote about a trip I took with the KCC (Korean Church Coalition) to Washington D.C to lobby for H.R 1771 (North Korea sanctions act) in Congress. This activity was very relevant to the field of political science, so I think that’s what might have separated me from the applicants with a 4.0 GPA and a 36 on the ACT.
If you are interested in, say, environmental science, I would strongly advise getting involved with some beach cleanups (removing invasive species, cleaning rivers, etc.) and taking AP Biology.
Unless your field of study is somewhat related to athletics, I don’t think sports will boost your application that much. Sure, it’s nice to have athletic programs on your application, but it doesn’t have much of an impact on your chances for admission.
TL;DR: State which academic field you are interested in and get involved in activities that can be linked with that field of study (this makes for a great essay on your application). Also, take a few AP classes (or honors classes) that are related to your field of interest. I don’t think AP classes should matter too much though (I only took 3 AP classes total, and I was admitted). Maybe retake the ACT one more time (I wouldn’t sweat it though, a 32 is pretty solid).
ALSO, don’t worry about clubs. USC doesn’t care if you just join a bunch of clubs just to “look good.” I literally never joined any club at my high school, yet I got into USC and Vassar. It’s all about quality over quantity. You have to selectively join clubs that are relevant to subjects you are interested in.