Little bit of common sense goes a long way... just 'play it by ear'... ask for some suggestions from her and during sex, learn by trial and error. She will take necessary steps to keep herself from getting hurt too much.
Have fun... this could be a great learning experience.
In regards to Indignant, some women don't care if the guy is big or small... they just want it rough because of the excitement of it and that pain mixed with pleasure feels good for them. I doubt a woman that would prefer a guy with a larger size and be slow and gentle would settle for a guy that is small, rough and fast.
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen