Re-take the SAT. Shoot for a 2000 (if you can make 1800, with a little practice you can knock out a 2000).
Study hard in all your classes and try to get at least a B average. I’m guessing you’re a junior? Take AP classes next year if they’re offered at your school. Take the placement tests.
You’re in sports. Is an athletic scholarship out of the question? Talk to your academic advisor about scholarship opportunities. Get a recommendation out of your coach.
If after you’ve done these things you think your cumulative GPA is too low to qualify you for a shot at USC, you can go to community college for 2 years, save thousands of dollars on tuition, room and board, take care of all of your general ed. requirements, get good grades and transfer.