Scared to try new things.

Raquel
My boyfriend of a year, wants to try something new in the bedroom..
I'm basically a open book, always willing to try new things. But this one made me feel uneasy.
(Pegging) 
I didn't know how to react when he brought it up.  He stressed to me he's not gay or bi.
But I had my doubts. (Maybe it's because I'm young? Idk) I'm nineteen. He's twenty four. I'm normally the one being "dominated", so I couldn't imagine things being reversed. I haven't been able to look at him the same way. 
Am I overreacting ? Is this not a big deal?
Any advice helps! Literally just a young girl needing some guidance.