It is so sad to lose a baby that was ready to be here. I am very sorry, truly. I hatch a lot, and you should know that duck eggs are tough to hatch, and thats no joke. Geese are the same.
I started with chicken eggs, which tend to be easier, and a bit more tolerant of humidity issues. The lose of one so close to hatch is strongly suggestive of humidy troubles. Why don't you get some more eggs, and PM me, so I can talk you through it. I would love to help you be successful, you are obviously very close to perfect there, or the egg would have died sooner. You are too be commended on getting so far. Waterfowl in general are just hard. I've hatched ducks for years now, and geese just this year the first time. I end up setting them end up for 3 full days w/o turning at all, then only hand turning, since they are quite sensitive. After 7 days, I spray them morning and night with a water bottle, until they are very damp. I also set them out onto a towel for 15 min. a day to cool and toughen up. (set a timer!) Once I began doing these things, I enjoyed excellent success. Its clear your temps are good, so your thermometer is good.
I hope you feel better soon, and please don't give up. I promise, if you go get more eggs now, and set them and do all the same except spray and rest outside like I stated, you'll have ducklings in28 days plus 2 days hatching time. (Khakis and Pekings are excellent hatchers, btw) Call ducks are nearly impossible.
