I'm alright at 3U.How confident are you with 3u?
It's probably better you stick with 12 units maybe, just for the first term. If you think that subject is really dragging you down, then drop it.
You can drop anytime in year 12 so remember that.
I'd wait until you are a bit further into your HSC before making a decision. If you are doing significantly worse in one subject and you are carrying 12 units, then it is not really worth keeping it.If I want to pick up 4 u maths then is it unwise that I do 12 units total for the HSC?
Especially if I'm doing not so well in one of my subjects.