Where did you get your info that the mean is 200 and standard deviation is 20? My score report says the mean for first time test takers from US and Canadian medical schools is 216 with a standard deviation of 23.
I also think that assuming that step 2 scores follow a normal distribution, that 31.7% of the scores lie beyond one standard deviation of the mean. Therefore, if your score is above one standard deviation above mean, you would have scored better than 84.15% of test takers. For first time test takers, this means that you would need a 239 to be better than 84.15% of test takers.
I find it hard to believe that people who have retaken the test or not from US and Canadian medical schools could pull down the average 16 points.