Not to add to your stress, but have you taken SAT subject tests? It is pretty much a requirement for MIT and Stanford. For USC it depends on what you plan to major in.
What are your SAT score splits? What do you plan to major in? Also USC doesn’t have EA, only application by Dec 1 to be considered for merit. Between MIT and Stanford you can only choose one to apply EA. This gives you a little more time for test scores.
My S19 was very similar to you. Top of his class, most rigorous classes (14 AP/dual enrollment level classes) , NASA research mentorship, very good ECs (but no national recognition), but his SAT scores were on the low end (780M and 630V). We also fell asleep on the whole standardized test thing. He didn’t take his SAT until June of Jr year and then again in Aug. He then spent the fall of his senior semester chasing SAT subject test scores and even tried take the ACT, but that backfired as he drove to wrong test site. Needless to say it was a very stressful semester trying to do testing, essays, applications, and a very hard course load. Of his top 3 schools (MIT, Princeton, and Ga Tech) he was accepted for engineering to Ga Tech along with some other great high ranked engineering programs. Even if his scores were higher, I don’t think he would have been accepted to MIT or Princeton as he really didn’t have a hook those schools were looking for.
What other schools are you considering and what are your financial requirements? Even if you had near perfect scores the schools you have listed are still very much reaches. Don’t base your overall success on getting into one of those schools.