Ditto Dat^^^I am glad that is over with for you and him.
I did not like how the cut didn't take the head completely off either, I've been told you have to basically cut and pull it off at the same time but there really is no need to take the head all the way off.
Sharpness of shears (or knife) can definitely be a challenge,
feathers and bone need incredible sharpness and perfectly aligned shears to cut well,
and feathers and bones can dull a sharp blade pretty quickly.
@KikisGirls is correct in that there's no need to actually sever head for euthanasia as long as neck is broken.