That's right - the idea that this is the "end" of the Mayan calendar and that means they predicted the end of the world is a modern urban myth. It is the end of a calendar cycle, and the next one starts the next day. Even Wikipedia (the cacher's ultimate reference tool ) has a good summary.
Rather than getting hung up on event names related to the "end of the world" etc., what about considering names involving related themes such as: Mayan Calendar, Mayan Civilization, Mayan Counting. The coin obviously used Mayan themes, so the name should match.
From my perspective, it would be better not to polarize groups with the event and coin name by using a populist but misguided theme.