Hi CLM,
First things first, if you need to close the survey so that nobody can answer it, you can do this via the Projects screen. Just click the dots menu on the listed project and hit Close:
If you need to roll back changes to a previous version, open up the project, select Tools -> Versions -> View Version History
The window that pops up will show all of the drafted and published versions, along with the changes made for each one. Select the correct one and select "Restore this version" to roll back to it.
Good luck!