Maybe don't give it as much consideration as you would other subjects, but still do try. You have nothing to lose (except maybe a little bit of time), but you will if say, you were asked to produce your HSC certificate for a scholarship or something (ALL your results will be on it, so imagine that one black mark..). Plus if you've persevered with that subject for 2 years, I don't see why you shouldn't give it your all
That way you'll never have regrets.
And yeah what people said too, you never know you may do better in it than you think. Plus, if you do 'mess up' another exam, at least you have the safety net.