Confess to God that you made a rash vow. It's rash because anyone who knows teenagers would know that you almost certainly couldn't keep it (and many of us would have told you that masturbation isn't much of a problem in the first place), Jesus told us not to make vows, and you were young enough not to understand the full implications of your vow. You ask God's forgiveness, and after that you are released from the vow. It's no different from God forgiving you for anything else.
I don't believe there's any official procedure for being released from a vow. The Book of Concord (the primary confessional authority for your church) looks at monastic vows, which share many of the features of your vow, and says simply that they are null and void. Lev 5 has you go before a priest and sacrifice, but of course sacrifice is no longer used for Christians.
However I think you'll feel better if someone who is in authority over you is involved. It's not needed, but having a parent, a pastor, etc, assure you that you're really OK will probably make you feel better.
Incidentally, I do believe you should normally keep your promises. I say promises and not vows, because I think Jesus said that you shouldn't vow. A simple promise should be enough. It's important for people to be able to trust you. The problem here is that you made a promise that an adult would have realized would get you in trouble. I want to make sure that you don't cite me as an authority when you promise to do something for your parents and don't
However even then, I'm quite sure your parents will forgive you when you fail (which you surely will from time to time), and that if you find something is too difficult to do, they'll let you out of the promise.