What should I do? I'm planning on moving schools in may of 2023. (I'm in S5)

At my current state school, I don't have any friends, and I don't get along with my headteacher because she has a horrible tendency to mislead, and some of my teachers have warned me of the 'regime' that she runs.

I had planned to move schools in s2, but then covid happened, so I was in lockdown for most of s3, and in s4, my school wouldn't let me move; in s5, I got rejected by multiple prestigious Scottish state schools.

Honesty, I'm quite disheartened at the fact I didn't get a social life like everyone else, nor did I get a happy time in secondary school so far.
Also, I feel that I won't get to catch up with my peers because I would have about a year left till university. (?)

Recently I've been looking at a local private school because it looks like a great opportunity. A slight problem; is that it looks a bit too small for my likening. (15 in a class)
Is this something I should be worried about?

Honesty, I want to get on with my education and my social life... But I can't.

No, I am not willing to try college. I wasn't impressed when I tried it.