If I accidentally published my app, is there any way to make it invisible again?

Yes. Please contact your assigned Customer Support Specialist or email [e-mail] if you have accidentally published your app and would like to "unpublish" the app until a later date. 

P.S. In case this didn't fully answer your question or want to see a live demo or ask live Q&A, join our Event Management Whova Academy! We host a live session covering the Event Management tool every Monday at either 9AM or 1PM PDT.