So there are ducks around. Hmmm. Did you see this?
https://www.backyardchickens.com/t/859788/diy-incubator
By the way - keep turning it over and over several times a day.
Do you know anyone with an incubator you could borrow, or who could do it for you? Are you sure it's a duck egg? There are DIY incubator pages around the 'net, and you could use the search box to see if you can find one here, too.
What an interesting situation!