You built this fast, and you tested it as you went. You know the login flow because you wrote it. You know which button to click first because you put it there.
That's the problem. You're the worst possible person to find the bugs in your own app, because you already know how to avoid them.
Real users don't know your app's unwritten rules. They'll refresh mid-checkout. They'll hit the back button after paying. They'll paste an emoji into a name field. They'll upload the wrong file type, or open your onboarding flow in three tabs at once because they got distracted.
None of that is unusual. It's just what people do. The question isn't whether your users will do something you didn't expect, it's whether your app survives it.
When did someone who isn't you last try to break your app on purpose?