Yep, it’s completely possible! I’m actually a living example. I went from a 3.4W (2.9 UW) GPA in high school to now sitting at around a 3.7 in college. I currently go to the best public uni in my state as well, so it’s not like I went to some random school out in the middle of nowhere. In short, it boils down to two things, how well you deal with change/how hard you’re willing to work and how you learn. For me, the latter mattered more than the former, since I was always a good test taker but I never had the patience to do any homework once I understood the topic we were covering. So going into an environment where doing the homework and going to class doesn’t matter as much and tests account for more of your grade, it actually ended up helping me rather than hurting. But this is just how I prefer to learn. However, as long as you’re willing to put in the effort, I’m sure you’ll do fine.
Also, you got into a UC no less, which means that you must have done pretty well overall in high school (even if you don’t think you did). Just believe in yourself and give it your best (I know this sounds really cliche) and you’ll probably do fine.