Chick only fills half of egg

[CassieH1112]

We have a small flock of bantam cochins and 1 average size road island red. She was a rescue. I decided to put one of her eggs in the incubator to see if they were being fertilized by my little rooster. Yesterday was day 21 and still no pip. The chick is alive but very small. It only fills 1/2-3/4 of the non airsac part of the egg. I have never seen this in other eggs we have incubated. Any insight?

 

[AltonaAcres]

Do you have pictures of the egg? That would help me assess the situation a little better.