If you check in with the "Webform" option (don't have the NSW app) it returns a confirmation code to that phone to enter into the webform. It gives you a confirmation screen with the name you've used easily checked by someone else. If you get challenged you might be asked to ID yourself (not sure how legal that is?)

Don't leave that webpage.

Scrolling down will give you a "check-out" button to tap on the way out. You have an hour to do this so make sure you remember.