19 year who skipped social life but wants to improve his situation. Any advices?

Sorry, if I make some mistakes but English is not my primary language.

I stopped being social around the age of 13. Always shy, stressed out and awkward around people I decided to escape the real world by playing videogames and other stuff like that. I never knew, and no one told me about the bad consequences this can have. I've had some pains created by stress during my early teenage years but the worst happened a year ago.

After the failed high school (probably because I skipped lessons as I didn't want to be around people) I'm now in a school for adults. It should be amazing right? Less time in school, adults who mind their own business and don't care about you. etc...

But I developed depression. Although I was capable to get it under control in a couple of months, thanks to exercise and the avoiding of verbal conflicts with my dad (mainly due to his ignorant, conspiratory views, in fact he doesn't want to discuss my problems and BLAMES THEM ON VACCINES). I feel lonely, there's no teenage humor, classes are small as f*ck and always changing so there's a minimal chance to develop relationships with people. Now I understand why group exercises were necessary...

There's possibly no way to go back to high school but would it be a good idea to make contact with these people after basically rejecting them? What's more embarrassing I never used social media. I want to make an account but why would they add someone with no friends? lol

The most frustrating is the fact that I know I shouldn't end up like that. I'm good looking, energetic, helpful and have some sense of humor but wasted my life on anxiety and the lack of confidence.