Lol an essay of 18.5 is pretty good, especially if you're in year 11, its a good start.
By the way, I'm not sure if I mentioned this before, but you have no need to memorise statistics exactly, a handy thing that my leading edge tutors taught me was, 'make them up' so long as you know the approx. This is best used for your globalisation essays, because hsc markers have no time, nor do they care about where your statistics came from. But just be sure to have a piece of statistic per paragraph...in fact I find it hard to not have statistics in eco essays, since this is exactly what you need to support your claim i.e. effect of inflation