No. Don’t take a gap year and re-apply. Start college in September, wherever is best for you.
Meanwhile, contact Cal and ask whether you can be re-admitted. You never know what you can get, by asking nicely. From your previous post, it looks as if you intentionally turned down Cal, so you’ll just have to beg to be put at the top of their waitlist, and maybe you’ll get lucky. But no matter what, start school in Sept, be it at Cal Poly or Cal. You should not waste your time waiting out a year and re-applying. Your results may be worse, and honestly, you will be wasting a year of youthful brain time, when you are best able to learn new concepts. You won’t notice it, but the brain does “mature”, meaning, it gets harder to learn new stuff. The difference for me between age 17 (started college) and 28 (started med school) was vast. In my late teens, I only had to practice something twice, and I had it mastered forever. At 28, I had to put it in and out of memory ten times to have mastered it forever. And it only gets worse after that.
I don’t know why you did what you did, but what you’re having now is buyer’s remorse. Get over it. Move on. Start school in September.