I have had ducklings hatch from the wrong side or middle as well. If he is still chirping I wouldn't do much at this point. Give him a break, he is probably worn out from working so hard, it can be quite exhausting, and I know mine always took lengthy breaks after the first major pip. Just make sure that he stays moist. Especially the membrane right around him. There is always a possibility that you will have to help him out, I have helped a couple duckling hatch, but that is always a last resort. Hope everything works out!!