A caveat on excluding overseas countries and territories would be justified. Aruba is close to Venezuela and Sint Maarten borders France for example :)
Not sure about the distance, do you count from closest bordertowns? Otherwise San Marino is also really close to the top 20. But maybe just outside it.
you all arguing that the antilles should be added, bu then we are alking about "The Kingdom of the Netherlansds" and the quiz is only about The Netherlands and not the Antilles
included. But Continental France is already there, so why include Sint Maarten? - If it weren't already included, I would agree with you.