Training and lots of it. I don’t think your petite build is the problem, there are lots of petite girls/gurls that can take 8” and more. You need to start off slow and allow your body time to accommodate such a large member. Get a small plug, wear it periodically until it becomes an easy and comfortable fit, then move up to the next size. Ultimately if you find a true Daddy Dom, be careful there are lots of fakes out there, it will not matter what your experience level is. He will guide and train you within the limits that both of you set forth prior to your relationship. We Daddies enjoy helping out littles achieve their goals and training them to be better subs.