I'd still finish proper tertiary education in any case if I were you. Even if you're not going to apply the gained knowledge, a degree shows proof of intelligence and discipline, which is useful even when you have a lot of experience in the job you may be applying for. Plus, once you start working there usually is no return, living the student life is fun, and it will all end when you start working.
And I totally get what you're saying too. I get real low grades for stuff sometimes too, and I always feel cheated when that happens -- like I spent all that effort for naught. I realize this may sound odd coming from an over ambitious straight A student, but it's true. Sometimes school can be ridiculously tough, but always aim to not let your self-confidence sway. Personally my self-confidence is prone to go on roller coaster rides though.