To be honest I had to look up what an Am Neo Bull was when you first came on here. I didn't know breeders were creating this boutique designer breed. Usually a Neo-Bull/APBT would be an accidental breeding as far as I knew.
I'm sure your breeder would be able to fill you in on what you can expect. Or you could Google it, like I did, and see what people are getting. Because you can't gauge a pure bred Neo to see how yours will look, or a Bullmastiff for that matter. A crossing of the two different Mastiffs throws a pure breeding weight, size, and temperament out the window. Add the APBT to the mix and, well, getting pictures of a Neo would give you nothing for an idea as to how it might end up looking.
And I'm sorry if I come across as being cross, I'm not meaning to. Your pup is a mix, and it will take around 12-18 months for you, and hopefully us, to see how it looks like.
If I would venture a guess it will be large, muscular and lovable.