Short of copy and pasting to Pages, you can't use it to backup. iCloud will backup your notes, but it won't save you from mistakes, since it will back those up too.
Depending on the account's note syncing wont work. They show up in a special email folder on the server, but like the backups it will also copy your mistakes. You could occasionally make copies of them there and use that as a backup, I suppose.
You could email your important notes to yourself (Notes has an email icon at the bottom), and keep a special folder in Mail for them. You'd have to copy and paste them back if you lose them, but it would offer a running series of changes. You'll also have to them manually to keep them from clogging your inbox; or if you set up rules on the server you might be able to use a standard title to automatically file them. Depends on what server you have.
My recommendation is to get a free Evernote account and apps for all your devices/computers. While it does not have the much desired undo function that would save you from your described problem, it does allow you to cancel the entire editing session of a note; assuming it's not a new note you can at least go back to the previous version.
Both the Windows and Mac version allow you to archive notes, which can server as a backup.
Even if you decide to go on using Notes for your basic note taking, Evernote comes with an email address that you can send those important notes to, giving you a backup of them on Evernote. But I'm guessing that once you see how much more Evernote will do for you, you'll be using it from now on.