If it is a larger egg, sometimes they don't fill it up, but they hatch okay. I have killed a few perfectly healthy chicks by cracking open eggs I thought had quit. I say if the egg is not smelling, leave it in there until a couple days after hatch due day. Sometimes there is a cooler spot in the incubator, even those with fans, and the chick may be developing just a little slower than the others and still be fine. Good luck! Post what happens. Oh, and if they are okay, you should e able to see them wiggling and kicking when you candle at that age if there is still room. If you GENTLY tap the egg or stimulate the chick, and it is just sloshy in there, it's probably a goner.