I don't know how serious you are about school or uni, but if you think you were capable of getting a higher UAI and have a rough idea of what kind of course you'd like to study, maybe repeating the HSC is a good idea?- you don't need to resit every unit if you don't want to, and you can do this at your current school if they permit, or at TAFE, or any other school which is willing to accept you as a year12 student.
But honestly speaking, I think TAFE Is probably a more suitable place for you to go if you suspect that your UAI, even if you repeat, will not be high enough to get into a course you actually want to do. At least with TAFE, you have more options open to you, the courses are more practical, and there are better job prospects for many skills than there are for a lot of the *cough* "not so useful" degrees.