I did crap in my first adv yr 12 assessment too (come to think, i did even crappier in my ee1 1st assessment ><). Don't worry too much in terms of fretting but make sure u learn from your mistakes. most important thing is to understand what u did wrong. In my case, i tried to memorise and essay and reproduce it in the exam (it was my first real test of closed book proper essay writing). Completely screwed up and realised that as tempting as it was, it was NOT for me. From then on, I focussed on understanding the stuff and didn't get so worked up in assessment situations.
Im not saying this is your problem but try to think about what went wrong and work harder correcting your techniques as u go along. Don't lose hope now. It's early days, true, but make sure you find out what exactly went wrong.