This may be a dumb questions, but are you not able to unpublish your sandbox? I hit publish to test it out and show a colleague, and then the publish/unpublish buttons disappeared. I have done this before on other courses, and I just hit unpublish. However, once I hit publish in my sandbox, those buttons are nowhere to be found now and it's permanently published. This isn't a big deal since I don't have students in my sandbox—it's more of a curiosity thing.