It is possible that you disturbed it while candling it, causing it to try to hatch early. If a baby feels endangered in the egg it will sometimes try to hatch early in order to escape, or sometimes babies are just stimulated by movement around them and will hatch (this is evident when you have several clutches due around the same time--one baby hatches and suddenly all of the babies start hatching out at the same time).
Day 50 is very early, but not so early that the baby can't make it if properly cared for during the first few weeks. As long as it is developed enough early babies can usually pull through--and your baby looks like it should be okay. Set it up as mentioned in a quarantine style tank, with papertowel substrate kept very moist. Hand feed if necessary starting in about 3 days or so and keep it around 75-78 degrees. Once it starts feeding well it should gain more strength and catch up to where it needs to be.
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