Sorry about your poor hatch rate.
What was your humidity at days 1-18?
Fully developed chicks that do not hatch is frequently caused by the humidity being too high during the first 18 days of incubation.
If the eggs dry down properly the air cells increase in size by quite a bit during incubation and the growing chick grows into the remaining space.
If the eggs do not dry down enough, the chicks will grow into the space not taken up by the air cell and grow too large to pip and hatch.
Also, on an egg that didn't dry down enough, the chick will pip the air cell and is met with a gush of fluid that drowns the chick in the egg.
Then it sounds like the first example, just too big to move around in the egg and get into position to pip.
Next time around you might want to try to lower the humidity by 10% and candle at days 10 and 14 to really track the drying down process.