Does pegging make you less of a man?  No.  Does it mean you are now the girl in the relationship? No.  Plenty of masculine men enjoy pegging.  Why?  Because it feels good and adds a new area of play to the bedroom.  Why else would  you have a g-spot in your ass if not to be enjoyed?  You can retain your masculinity AND enjoy your prostate.  You can even dom from the bottom if you like.  There are no rules when it comes to pegging so enjoy it and don't worry about stereotypes and misconceptions.  
Tell her what you want and take control from the bottom!