Are you worrying over nothing? Probably. Men are a LOT less critical of women's bodies than women themselves - especially when it comes to your own! He's clearly keen to get you naked, and so unless you're hiding a whale-load of blubber under some serious corsettage, it's unlikely he'll run away screaming. It's not hard to get an idea of what someone will look like naked if you see them in fairly tight clothes, so he'll probably know what to expect mostly. So on that front, I'd say try not to worry, especially about comparing yourself with his ex - he's with you for a reason and that's more than just your body (I'd hope).
However, the fact that you feel uncomfortable about what he's saying might be an issue. I'd mention to him that you feel insecure when he says things like that (and yes it does sound creepy!)