I may have felt similar when I was your age. But didn't have the maturity to change for the better. Also, although I found to the Pali Canon somehow, I didn't trust today's Buddhism and thought after 2600 years, whatever institutionalized or organized practice there is today and calls itself "Buddhist" must be flawed and can't be taken serious.
So I spent seven years hating and pitying myself and speculating about enlightenment without any practical approach to the life that I had messed up. That's a thing you should not do.
What others said here about Metta Bhavana is certainly very useful. I myself did a Metta Bhavana retreat about a year ago. If anything helped me then that. Following the instructions and doing formal meditation without a teacher, at least for me, is very hard to do. So visiting such a retreat might be very very helpful. At least you are told what to practice all the time, so you can do it with a humble attitude.
The greatest difficulty I had was my arrogance. It all looks and feels so artificial and I had a hard time subduing my contempt. But it was part of the practice. And I went there because I was desperate. And it was an eye-opener.
And otherwise, what is probably more important, as others told you:
1. Do good things. Even if at the moment you do not see much good you can do. Maybe you can't. But the time will come. Possibilities will come if you keep yourself ready and don't give up.
2. A friend joking that you are too bad to be a Buddhist, things like that, trying to "be a good person", you just need some humble self-esteem to go through that. Cynicism is a bane in such a situation. But if you don't get friendly support you must go without it. People don't share your pain, your guilt, your conscience. So it's easier to joke around. But you just stay clear, make the best of it, endure it.
Blahblah. Not knowing anything better than you probably... but just trying to encourage you to do the best. Even if everything is dark.