"Hide the unlocker" hides the unlocker app.
Now, there is no reason to run the unlocker past the initial activation.
Remember that the unlocker is just that -- it unlocks the same, base, free app to "Pro" state.
To use the app, please run the base, free app's icon -- it's labeled as just "AquaMail" in the device's apps list and maybe on the home screen.
Its title bar should now be "AquaMail Pro" (but I have no way to change the icon's label in the apps list or the home screen).
If you feel like you need to get the unlocker's icon back -- then yes, please uninstall / reinstall just the unlocker. Google Play should not ask you to pay again.