@Seminolegirl apologies if anyone sounded harsh. We sometimes tend to jump in with specifics and our bedside manners go out the window.
We all want to help, and it's great that you are trying to save a duckling. So sorry about the lost pekin.
Anyway, the duck eggs that I am currently incubating were in one of my ducks nests for several days, cold overnight temps, near freezing. She would sit part of the day, but not overnight. I suspected the eggs were no good, getting that cold, so I took them. To my surprise, they are all developing.
So the low temp that yours has been at may cause some delays, but I agree, give it a few more days, try to get the temp up closer to 99-100, and see how it goes. I despise trying to read those merc thermometers, but it's probably a very accurate one. If you could fine a digital one that is submersible (at least the tip or gage part), you can run some hot water, get it to about 100 degrees on your merc thermometer, and compare the digital one. It makes incubating much simpler.
I really do wish you the best of luck!