You know, why don't you measure a similar item you have that you like the fit of. You may find that it's actually slightly smaller than you measure. An inch or 2 less is often a better fitting sweater or top than one that's the same size or larger. I think you'll be fine either making it in the largest size as is, or with the next size larger needle (which could make it too big for you). I measure about 45" and make my tops with 2-4" negative ease (smaller) and they fit very nicely without doing any waist shaping.