That takes some getting used to, indeed...and is something that tricks like the positioning of the hips especially help with....
Once again, I'm convinced that we're all a bit different, and some of us can never take quite that much, and a few of us not so much at all. I have now had the pleasure and opportunity to have been around ten girls taking their first BBC, and we have had one who,though eager and totally into it, just wasn't going to be able to take more than about half of him, probably due to a combination of girth and length, and several others who seemed like they would come close but never really quite get balls-deep with a real BBC...unlike what you see in most of the porn (though if you look at my comments, including about one of the Blacked movies, there are some vids that show the reality of girls who can't take it all).
I'd counsel patience...and acceptance....
Lanie