This is a hard question - what do you do as an adolescent when your social skills are terrible. I don't actually know a good answer. The best I can think of is to find different groups to socialise in via hobbies/extracurricular activities to just get practice.
I have a hard time believing that the optimal solution really is to isolate yourself and learn them only as an adult (because, indeed, adults are easier to get along with), because that means both your adolescence and the first couple of years of your adulthood are liable to be awful.
School did indeed suck mayorly, even though I did have a few friends. (I wasn't that terrible, my problem was mainly just shyness.) I still wouldn't know what to tell young me, though. I guess I'd start by telling her that this is something that can be learned in the first place. Your idea of finding other groups outside of school is good, too. Unlike school, you can always drop those if they don't work out.
A brief essay intended for high school students: any thoughts?
If you go to school, take the classes that people tell you to, do your homework, and engage in the extracurricular activities that your peers do, you'll be setting yourself up for an "okay" life. But you can do better than that.
The school system wasn't designed to help you achieve your goals. It wasn't designed to optimize student welfare in general: it was cobbled together by many different actors with many different goals, from politicians to teachers to parents to colleges. It often suffers from inadequate resources. Even if the school system were optimized on average, the one-size-fits-all approach it takes means that it wouldn't be optimized for people who differ in any relevant respect from average. Compared with what you can achieve by carefully thinking about what your goals are and how you can achieve them, following "the system" fares poorly.
By putting you in this situation, society has fouled you. Yes, as you suspect, a lot of the stuff you learn in your classes is crap. And yes, as you suspect, the college admissions process is largely a charade. But like many fouls, this one was unintentional. So just keep playing. Rebellion is almost as stupid as obedience. In either case you let yourself be defined by what they tell you to do. The best plan, I think, is to step onto an orthogonal vector. Don't just do what they tell you, and don't just refuse to. Instead treat school as a day job. As day jobs go, it's pretty sweet. You're done at 3 o'clock, and you can even work on your own stuff while you're there. — Paul Graham in What You'll Wish You'd Known
Some subjects are more important than others
High school can give an illusion of democracy between the different subjects you study: they all seem to get equal weight in class time and in grades, so you may believe that all subjects are equally important to study. This is not true even in general: some subjects are more important to study overall, and within each subject, some topics may be more important than what school seems to suggest.
Because the method of exposition and choice of topics in school is likely suboptimal, it generally makes sense to learn the important topics well ahead of time, and deal with the others as needed to do well on the courses.
It's important to choose your extracurriculars well
Many common extra-curricular activities (in particular, many school clubs) are not the most productive uses of time. If you go with the flow and sign up for the activities that the people around you are signing up for, you may sacrifice the opportunity to develop yourself and accomplish far more.
Consider alternatives to high school
Consider homeschooling and online school. Depending on your situation, these may be superior alternatives to regular high school for you.
This post is a modified version of a write-up for Cognito Mentoring.