not sure about maths, or about your school etc, but at my school they deliberately make the trials much harder than the actual HSC so that people are used to the pressure and the questions and everything when it does not hold as much importance. They also do it so that hey can discern people's rankings easier, becuase they'll all be getting different marks, instead of everyone doing well and having the same ranking.
Do a trial paper and HSC paper for yourself and see, personally for maths i find the trial paper harder than HSC but for other subjects they are usually the same.