This same thing happened to me!
Accidentally deleted all of my important copy...in one click.
I did manage to get mine back, however.
I recently activated a new iPhone. I kept my old phone and turned it on AWAY from my home internet so the app could not sync with the newly deleted note.
I opened the app, and boom, all my content was still there on my old phone. Copy and paste! I got lucky, but figured this might help someone.