Did you use a default instance name or a customized name ? I think i have seen this once where i was circling around the same configuration screen and then passed it when let the installation to create the new database with default instance name...
Try this, Just to make sure if your setup is correct, can you just let the installation to 'Create a new database' and WITHOUT specifying any 'Intance Name' in the Instance Name text field (Leave it blank), Installation will then create a database in the name of 'appstream'. Lets see....If it succeeds then we might be up to something in mapping the new database you created manually in the SQL system.