Four of my friends forgot to do a whole quarter of the maths trial exam, but honestly, if you've done well in year 10 in all your class and assessment work, or even if you've just done average, it ultimately doesn't matter even if you wrote I'M STUPID on all your papers; because its your school that decides if you go to the hsc or whatever courses you chose, and they decide that on what they know of you. The hsc is what is important.
(nice little aphorism there!)