The technical contact of that project should add you to the project and thus give you rights to access the model.
Regards,
Ronald
[EDIT]
If you created the project and thus are the technical contact you must file a support request.
seems like a bug to me. Since you created the app yourself, you should be tech contact and have the Scrum master role.
How did you create the project, from the platform – http://home.mendix.com or from studio pro – local installer?