I was in a similar position 3 years ago
as ATAR release date approached I convinced myself that I didn't work hard enough and didn't do well enough in my exams to even get a 70. I ended up getting a mid-high 90s score and all that stress was for nothing!
Our brains are really good at second guessing ourselves and over-analysing everything we've done and then amplifying all our worries so they blow out of proportion. There's nothing you can do now to change your scores (whatever they may be), so what's left is you just need to take your mind off ATARs (easier said than done) and try calm your mind a bit. A trick I learnt with my psych that has been great is when I have thoughts that make me really anxious, I write dot points down that are for and against it and look at the facts - I find this usually helps me see that my anxiety over whatever it is happening is out of proportion and it teaches me to adjust my emotional response. I'd also suggest trying some mindfulness apps or something like that! Anything that can help distract you, really.
I'm sure you're gonna be fine! 😁