That particular ticket isn't sold any longer. Yes, the MK one-day cost more than a one-day to the other 3 parks. I see 2 possible options:
1) assuming it has not expired, they may allow you to use it as-is, but no refund of the extra paid
2) or since it is no longer sold, they may require you to "upgrade" to a current one-day ticket. Not necessarily a hopper unless you intend to hop.
Let's hope for option #1.
Enjoy your vacation!