Boyfriend wants to experiment with no protection...?

So earlier today my boyfriends asks me if he can put his penis in without protection just to know what it feels like, and then he would continue with a condom. I'm definitely against it, because I'm in no way wanting to be pregnant. Am I acting silly? I hear too many stories about people messing around unprotected and getting pregnant accidentally. What are the chances of me getting pregnant by attempting this? And how could I tell him I'm not ready to try that? Does anyone have expirience in the situation?