This is not enough, you need to make a proof of the date it was created, not showing for people.
You can print it out and send a letter to you self and never open it. You can email it to your self to make sure. You can publish it as eBook or document in Internet. You can publish it on blog or similar types.
Copyright is all about: You can proof when you wrote it.
I'm busy working on my blog posts. Watch this space!