You will get your the results given the situation if you stop worrying about everyone else around you and just focus on yourself. The lack of resources is a concern, but you can befriend someone who does get those practice exams or buy them yourself. The very best resources (VCAA exams, AN) are free anyway.
I think that the scores of private school children predominantly benefit from the fact that their parents value the education system and that they are around others who also value the education system. Just because you are deprived of this, doesn't mean you can't do well but it does make motivation more difficult. You clearly already have the motivation, so you can ignore everything else.
My school consistently only gets about 3-4% of study scores above 40. what should i do?
so many lazy retards doing drugs, drinking alcohol and undertaking pre-marital sex to be bothered studying...
I'm weary of calling them 'lazy retards' just because they value different things to you. Besides, if their only true problem is laziness, then all of this socio-economic analysis shouldn't matter as long as you aren't lazy. It's unlikely that laziness is the problem, probably it is disenfranchisement and being resigned to the idea that regardless of what they do, they won't be able to achieve all those arbitrary hallmarks of success (high ATAR, high paid job, etc.). It takes a lot to overcome that.