@LauraGrimes123 , you built a canvas app from Power App, so the power app is a product from Microsoft so you should have a license for at least Office 365, so that you can login to https://make.powerapps.com page to create/design/publish the app, right ?
Then in AppStore, there an App name PowerApp which is also Microsoft Product, this one is to use the app that you made in the studio. User will download this in order to use the app that you made and they need to login first, login mean they need to have a office 365 account with at least a office 365 license assigned to them. This is the first thing to know.
When you mentioned anyone can access it. I afraid that only user that have at least a office 365 license to login to the Power App, and the App you made should share to that account also, and you can only Share your app to the account that in the same tenant with your account, that mean if the user office account is in another tenant, you can't share the app to that user :).
That what I understand, hope this explain can show you thought.
