Massively editing post...
In short, yes, 90 is hard to achieve. Lots of people dismiss this, but the reality is that for every person our age who scores 90+, 9 won't. Even 80's incredible.
That said, 90 is definitely a possibility if you work hard and get lucky.

Do your best - try not to focus on the score. I used to be a complete perfectionist back in VCE, but really, anything that'll get you into your course is fantastic. You don't need a 99.95, a 95 or a 90 to be intelligent. You are who you are. VCE doesn't change that. That's something that quickly becomes apparent once you realise that no one really cares about your ATAR anymore - heck, I'm going to go to a university where almost noone outside the person in charge of Australian admissions even knows what an ATAR is.
Best of luck
