Yes, this means that you have until the 19th June to submit your supporting documentation for your application.
Pretty straightforward. Otherwise, be smart and call them.
Can you still access Online Applicant Services from the UAC main site? Other than telling you that you can change your preferences up until the 19th, I don't think many people here can help you further.
I'd suggest calling UAC first on (02) 9752 0200, tell them your situation and find out where...