Luis,

If I were in your position I would file a small claims lawsuit asking for either the money or the copyright to the work I ahd done sense it was NOT for compensation. That will, if you win, get you either your money or the ability to sue him if he uses any of your work on his "project".

Then I would watch him like a hawk, praying that he used my code and that his project was fantastically successful. That way the big suit would get me a lot of money.