I'm a newbie myself so I'm sure others will be able to help you more but I've replied as I started pretty much the same thread in ducks!
I wasn't good at judging what I was seeing when candling and was convinced the air sac was at the pointy end. It wasn't! The egg contains some fluid at the point egg until the chick / duckling has grown completely into the egg and I assumed it was the air sac.
I had one egg that had a lot more fluid in and sadly that was a no goer. One thing I noted was my good eggs all looked the same even though I couldn't make out movement at that point or the air sac. I had to accept that as I could see healthy veins that they were alive.
I found that the air sac was at the top by candling in a very dark room with the torch pointed down slightly but sidewards on. My ducklings are khaki Campbell's so they are dark and definition isn't easy to see.
As I said I am as new to this as you are but if your chicks are moving and you have good veins showing at this point I think it is what it should be and you just can't see it. I've read no end of different advice on the whole process and I wound myself up and became so worried until I accepted that no two people's experience is the same. We can just tell each other about that and we can learn too but we have to accept it is only general as their conditions aren't going to be the same as yours.
My advice is to stick to the textbook approach the first time and learn from it. Lock down as you are supposed to, I was told to mark the lowest part of the air sac arc with a cross but I found that the actual the egg positioned itself naturally with that at the top (rolled into place on the table with the cross on top). Raise the humidity to the level for your incubator and the recommendation for the breed and let nature do her job. Don't be tempted to keep messing.
The chicks have a strong instinct to survive and know what they are suppose to do - unlike us
Try and relax as you will learn from this as it goes along.
Good luck!
