Filling the shell is a good sign. Leave them be and just wait. Sometimes they can take a long time to hatch. Never had duck eggs, but if they are like chickens, patience is a virtue with them. Not familiar with that breed, but I think some take up to 32 days to hatch.
i raise ducks just make sure your temperture and humidity is right you have to raise the humidity at the 26 day they can take longer if your bator was running a little cool .leave them in until about 32 days if they dont hatch check one
Most duck breed take 28 to 32 days. Call ducks take 26 usually and Mescoveys usually take 35. It is kinda like the bigger they are the longer they take. My call babies started on day 26 with 1 tiny pip and it took that baby almost 32 hours until it finally hatched. It took the second one about that amount of time too. Jenn