The FIFA rankings are a load of rubbish that unduely promote teams that play a lot of games and teams that play a lot of qualifiers in the weak CONCACAF group. The US are not one of the best teams in the world (perhaps between 15th and 20th at a wild guess).

That said, +6600 or better is a decent price for a small bet. As Greece showed in Euro 2004 anything can happen in a small tournament.