If its not retroactive, then network participants have already received it. What they choose to do with that data is totally beyond your control. You can ask that they forget your secret. If there's a small enough population that received the plaintext (ideally one, as in a DM), then you have a chance, but no certainty, no matter what we do.
The point of NIP-09 is to delete already broadcast notes. If you haven't broadcast a note yet, you don't need NIP-09. Unless you're using Amethyst. Then your drafts will get you in trouble regardless...