Relax, OP you still did exceptionally well! As for your dilemma, does ANU advertise a 'minimum' ATAR? This is a feature quite a bit of universities have adopted in the wake of the (SMH?) article that exposed how so many of them were admitting people well under the cut-off. This would be a helpful indicator.
In any event, I look at it this way. Your score means you are near the top of the state (or close to it). Out of those thousands of people, how many want to do Law? A quick browse of the top students on the Distinguished Achievers list at places like James Ruse shows *a lot* of top-scoring students with subjects like Chemistry, Physics and Mathematics Extension. While these do not exclude a student from pursuing law, you'd think that the preference of these people would be to a more openly Science-y or Maths-like degree.
Next, how many of those students will want to do Law at your specific university? Although ANU is well-respected for its distinguished law school, it *is* in Canberra, not exactly the most accessible location, even for a Sydneysider. This means that the competition is perhaps a little less fierce than comparable city universities.
Both of these questions narrow down the competition somewhat and mean you have a real shot at getting in IMO, even though you are under the cut-off. However, allow me to emphasise the fact that this is all simply conjecture off the top of my head; nothing I say is fact. All I'm just trying to do is put some ideas out there for you to think about.
Good luck and best wishes!