Cheeky,
Being a writer is like being an actor both male and female. You assume roles that you normally wouldn't think about doing in real life. If you ever watched True Blood the series, you would see a lot of this type of sex between the same gender. It's just a fictional story after all, and you should be able to let your mind roam through the halls of your imagination. One day I might even try an M/M story. Since I'm writing to you on this, I should practice what I preach, right?
Read some of the F/F stories (if you haven't already) and get your feet wet. No one should push you into something you don't want to do (and I don't think anyone here will), it's just a thought as Goodgulf described in his post.