@Hilary Davis I have experienced this error before when saving my changes to a Template but it occurred when I lost internet connectivity in the middle on my edits. Basically the changes that you made are likely unable to be saved due to the scenario that during the Template edits you may have dropped connection to the internet momentarily.
Typically you would need to close the browser and re-login to the DocuSign UI and make these changes to the Template again because there is a good likelihood they did not save.
Regarding the Template protection, the bet option is to set a password on the Template under the “Advanced Options” of the Template while in Edit mode. This means any other DocuSign Users with Template edit permissions would need the Template password “if” they tried to edit the Template you own.