It can be difficult to change someone's opinion, especially after such a relatively short time. Go with your gut - if you think he might use it against you, he probably will. Enjoy your new opportunities and don't worry about it too much. Your actions will speak for themselves. As for what he may have told your new bosses - they hired you, didn't they? They obviously saw something in you that he didn't, and at some point down the road he'll smack himself for being so shortsighted.