Is this a hard ticketed event? We are going to
MNSSHP and I had to go in and manually add in each ticket and assign each ticket to a member of our party in My Disney Experience. MNSSHP is a hard ticketed event, but I was able to link it to our account in this way. Just go to "Reservations" and "add a ticket", then type in the ticket numbers on the back of your cards. Then it will ask you to assign a card to each member of your party.
I went ahead and spent the time doing this hoping that when they scan our MagicBands upon arrival to the MK the morning of MNSSHP, they will just band us at that point so we don't have to return to get banded at 4PM.