Whatever you do, make it something you care about. You have to spend the time doing it, and the odds are very high that it won’t make a difference and you won’t get into the highly rejective schools no matter your record. That’s the way it is…too many highly qualified students applying to too few schools. So, do it for its own sake. If you get in all the better. If not, you won’t feel as if your time was wasted.
FAR more important is your GPA. It’s the first litmus test at every school. Your freshman grades have probably already pushed you out of contention at competitive programs like Cal Poly that use them. Most schools don’t, so take it as a wake up call to raise it if you want a chance at competitive schools like the ones you’ve mentioned.
Good luck.