You were correct! The odds of you getting higher than 19 with one card whilst on this set-up is approximately 1/7, as only an ace or a two could better your position within a singular card. Even then, you would need a combination of 11 or 12 which is only obtainable in 16/169 different ways, which is over 10/1 odds. Would you back a 10/1 bet if you knew the maximum you could get was evens? We would sincerely hope not.