HELP!! Duck has pipped externally at the wrong end!

[LouiseFiveJ]

So last night i candled the eggs due to not seeing any movement and them also being overdue, i noticed one in particular was pecking away into the air sack and so i put it back into the incubator wen i did this i could then hear it chirping away, does that mean it had pipped internally? so this morning i could still hear it and was able to candle it from the outside of the incubator where i could still see it pecking at the correct end in the air sack, i have now just got home this evening to find a crack the wrong side??? on closer inspection i don't believe i can see a beak but i can see slight yellow feathering so im slightly confused as to whats happening and what to do? any advice would be much appreciated this is my first duck hatch i have previously done chickens.
Also just for information they are khaki cambells

Thank you

 

[Ravynscroft]

Pics would help determine what is going on... any chance it rolled around and was cracked that way? Could you see a bill in the air cell during previous candling?