'Bullshitting' a graph? how is this possible?
You shouldn't have to be plotting a graph with real values in an eco essay anyway so you would either know the graph or you wouldn't. Whatever graph you 'bullshit' will convey some kind of meaning to the reader so you can't exactly pull it from thin air. It has to either come from something youve seen before, or you can quite legimately come up with your own representations of economic theory in the form of a graph if you are clever enough.
As for statistics:- trust me. By the time of the HSC you will know every satistic that you could even think of. You have plenty of time to study between the trials and the HSC and if you dont have a good grasp of real statistical values then you are lost cause. For Australian statistics you should know them accurately as the marker will almost certainly (unless its some obscure statistic that is uncommon). Consider that the markers read many many essays and will be familiar with the numbers.
As for statistics relevant to your case study:- this is a little less clear. I would still not encourage making up statistics, but because the data is unlikely to be as reliable (as different students may be using non-current data), and of course there are many different countries that can be chosen which makes it harder for the marker to remember all the figures (much less know who is telling the truth). But certainly, they arent going to go and research your stats in the middle of an exam marking session.
For your in class assessments, maybe your teacher will be a little easier on you at first, but they will start to pull you up on things like false statistics as the year goes on. But thats ok because you will get better as the year goes on.