I dont know
Can you see or hear a fan going round to circulate the air? Can you tell us what brand the incubator is?
It makes a difference as a forced air (with a fan) incubator is set at 37.5 degrees celsius but a still air incubator is set just a fraction higher so depending on which you have, you may be fine or not.
What is your humidity level? You haven't mentioned that at all and it should be up around 70%.
Also, when calculating your hatch day, did you count the day you set your eggs as day one or the following day? It should be from the following day....24 hours after the eggs are set. So whatever day of the week you set your eggs, they should hatch three weeks later on the same day HOWEVER fluctuations in temps and humidity can slow them down so it's important that you are patient.