I can only imagine sex as a guy

I'm a girl and the though of sex has always disgusted me until I imagined my self as a guy and this was the first time it really felt good to masturbate (age 19) I did it by imagining I have a c0ck and put it in a straight girl but I would be sub. Even seeing myself dressed as a cute boy turns me on so well but I would not want to get a sex change, or wer a strapon, because I wouldn;t be a real boy then plus I'm ok with being a girl I'm just wondering if it's normal that I can;t see myself ever having sex except in my fantasies where I am a guy.