Is it impossible to get into a UC school?

So I'm mainly focusing on the UC schools when it comes to college's and the recommended GPA is at least a 4.0 - 4.2 or higher. freshman and sopre year I did average. nothing bad and nothing too great either. junior year, I'm going to be devoted to my volunteer work, extra curriculars, and academics. I'm taking 3 AP's this year and plan to take more during my senior year. I've already hired a great PSAT/SAT prep tutor to help me prepare for the 2 exams later this year. If I do get a great SAT score... say like a 1950 or higher... would it still be possible to get into a UC school like UCSB or USC? Those 2 are the main UC schools that I'm interested in. Also, do UC schools check your freshman and sopre year grades? I heard they only check junior and senior years.