When you open the URL without any other options (q=...) then the default questionnaire will start. Please set the default questionnaire carefully in "Compose Questionnaire" -> "Manage Questionnaires", maybe save again, even if it's set correctly.
Please note, that the access settings are configured separately for every questionnaire. So, you could have 2 questionnaires with different passwords, a public one and one that is reserved for internal use.