google atar calculator and see for yourself the marks that are required for your desired atar. Its helpful because you will be able to adjust it basing it on how good you are at specific subjects.
any atar is possible with any combination of subjects, however, you might want to check with your school if you are even eligible for an ATAR. from memory, you need to undertake at least 4 different subjects to be ATAR eligible, but you only have 3 at the moment (assuming history ext is included with ancient history). please check with your school/UAC ASAP, because you can’t get a 99.95 if you don’t get an ATAR in the first place, regardless of the marks you get