Don't get yourself down like that. I moved from 2U to general the week before the exam... luckily I was fine, but my maths teacher says people don't usually get what they're capable of at first, because it's a big transition. Sometimes they're cocky and reckon you can do ace without working - not saying you did that though.
Anywho. You've messed up - but find out what you did and make sure you don't do it next time when it's worth more.
I choose to look at it this way - I could've dropped 2U for year 12 and done no maths, or I could move to general, work hard and do really well. I know which is better for my UAI.
Stick with it, tell yourself you're smart and you can do it - once you're used to the move and stop seeing yourself as a dummy, you'll do well, I betcha.