If you had to create a user account after setup ran, it is completed. You should be able to login via yourdomain.com/admin
The maintenance mode is enabled by default when running setup t o avoid site aceces during that. And also is kept after the completed setup which is especially useful after installing an update so you can test all works before opening the site again.
If that really does not work, open the config file in /zp-data/zenphoto.cfg.php and find the entry for `$conf['site_upgrade_state']`. If it does not read `$conf['site_upgrade_state'] = 'open'`, change it to that.