misc etc had an interesting, scientific answer, but I see his data come from the enquiry of Lifestyle condoms, made on 301 volontary student among more than 1000 ones (400 were volontary, but 100 would not get excited enough so that medical staff could not keep there measurements as valid).
But, if you go through urology journals around the world and make an average of Caucasians medically measured, you find an avergage of 13,9 cm (5"5), and average standard deviation is 1.9, since only twice recorded : 1,7 in Greece and 2.1 cm in Cancun (Lifestyle). And average girth is 11,5 or 11,7 cm (4"6).
I propose You recalculate on these bases.
I would say you are very big and your girth over average though not impressive. This is enough to be satisfied.