Know nothing about the Qld app, a serious design flaw IMO. Perhaps it was deliberate? QR check in's are primarily used to generate testing lists anyway.
The NSW app:- you don't have to return to where you checked in, do this instead (from the NSW website).
"To check out:
open the Service NSW app
go to COVID Safe Check-in
tap the Recent tab
tap the Check out button."
I assume it links to the last check in you made. The longer you leave it the higher the risk of getting pinged.
However, if they checked in for you via the webform I guess you'll have to go back to them to checkout. Must admit I don't know how that works as they would either have to retrieve the original record or re-enter your details and tap a "check out" button.