I would email him and ask him to mail the journal entry to you, if you really want it back.

On the other hand, I don't really understand why you want it back. He can't do anything with it or show it to anyone, so whatever you wrote is not going to get out. People are probably more likely to see it if it's in your possession. I'd just cut my losses and forget about it. But then I have boxes of old notebooks that I never look at.