A lot of people at my school put their half yearly marks into atar calculators and had atars of 50/60
Most of them ended up with mid to high 80s, and even a few 90s
Nothing is impossible if you put the effort in to obtain the marks you want.
Putting your raw internal marks into an ATAR calculator will get you nowhere because the marks are heavily moderated. However, like you said, there is still hope.