Cutting at day 49 is early for an inexperienced breeder, especially at lower incubation temperatures. When you cut, you open the inside of the egg to a warm moist environment that's perfect for bacteria growth.
I'm sorry you lost the baby. Breeding ball pythons requires a lot of patience. I know I'd love to see what is in the eggs way sooner than I do, but that isn't in the best interest of the babies. And, me knowing what is in the eggs early doesn't change a thing. They are what they are, no matter when I cut.