An x-ray of your pelvis tells you exactly nothing.
It only gives a picture of the way your pelvis sits when it is not in labour. Labour is a dynamic process and the pelvis, being a non fixed structure which stretches and opens as the baby descends will only be seen at it's fullest potential while you are actively birthing a baby.
There are many positions you can use while labouring to help widen the way your pelvis is opening, but this is different for every woman, and often different for every baby as well. The mothers intuition while labouring with regard to labour positioning (hands and knees, squatting, walking etc) is incredibly important, as her body instinctively reacts to the pressures the baby brings to bear as it is corkscrewing out of her body.
An Ob sitting in their office telling you point blank your pelvis is too small is not only saying something that it would take a psychic to know, they are also in my opinion committing a huge sin, which is making you begin to lose faith that your amazing, custom built body is in some way defective. That is simply NOT ok, nothing of the sort is even remotely begun to be seen, and they are SO often proved to be dead wong about these predictions. This kind of thing makes me extremely angry.
Another really good resource with heaps of info about your amazing pelvis, is The Pink Kit http://thepinkkit.com/the-pink-kit-package.html