I have never gone by the "wingspan" method for determining draw length.
Best thing to do is draw the bow back and find a good anchor. Let a pro or someone with experience look at your anchor and determine if it is correct. I have even looked in a mirror while at full draw before. It is very easy to think you have the correct draw length, but in reality it is too long. Corner of mouth and tip of nose is a good place to start for an anchor.