What are my chances of getting into University of Southern California?

I’m a senior in high school

1260 on the SAT (Superscore)
4.1 GPA at a very challenging college preparatory high school

I have taken 3 honors classes and gotten As in all of them
I have taken 4 AP Classes and gotten a B+ or higher in all of them.

Extra Curriculars:
-I am on the Board of Directors (and serve as the treasurer, giving me financial experience) for an entirely youth-led 501©3 nonprofit organization called Youth Ending Slavery. I have been a part of YES for 4 years.
-I have been a JV member of my school’s XC Ski team for 2 years and a Varsity member for 1 year
-I attend the Human Rights and Women’s Equality clubs at my school and have since freshman year
-Over the summer I work at an art camp for kids
-During the school year I volunteer with the Outdoor School program in my county and spend a few weeks a year living in cabins with 6th graders and teaching them about natural science

As for evaluating yourself as an applicant to USC or any competitive college or university, I recommend first reviewing the following excellent thread on this topic…

http://talk.collegeconfidential.com/university-southern-california/1558825-what-are-my-chances-read-this-first-p1.html

good luck