I made a free-for-teachers account and would like to create a public course, available to anyone with the URL. I followed the instructions here: https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-customize-visibility-options-for-a-cour... but my course visibility option cannot be changed. It asks me to contact my administrator. But this is simply a free-for-teachers account, not affiliated with an institution, so I don't have an administrator to contact. Have I overlooked something? Or is what I'm trying to do not possible?