Hiya Margaret and welcome to planDisney!
Being sick is no fun and it's infinitely worse during a Walt Disney World Resort vacation. I've definitely been there and I'm sorry you had that experience. Unfortunately, because you had already started using that 3-day
Ticket, that last day is forfeit due to Tickets being date specific. But between you and me, I'd try pleading my case with an email to the Cast Members over at guest.communications@disneyworld.com. Just let them know your situation and see if they can help. It ain't over until the Cast Member sings!
If things work out in your favor, let me suggest booking a September stay. The crowds are usually lower, although with the
50th Anniversary Celebration in full swing, who's to say! And the
EPCOT International Food & Wine Festival continues to knock any other time of year into second place in my humble opinion.
Margaret, take care and I'm wishing you lots of pixie dust and good health on your next visit!
Happy planning!
Taylor