The pic of the plastron is a bit dark to see if there is any rot but it looks fine to me, just normal coloring.
Try to oost another pic that's a little lighter.
Your species almost never gets shell rot, but they can certainly pyramid. Looks like your baby is being housed too dry. Or maybe outside all day in warmer weather?
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There is a temperate species care sheet and a heating and lighting breakdown at the bottom of that thread.
We can better evaluate the plastron when you post a pic with a little better lighting, but its very unlikely to be shell rot.