Do you know which species of flat rock scorpion it is?
Flat rock scorpions are well known for fasting for long periods. So long as you are providing the scorpion with correct living conditions then I wouldn't worry yet. All scorpions will regularly hide away for 3 days, and flat rocks will do this more than most. They are adapted for living in thin rock cracks, and will spend most of their life in one, sitting and waiting for prey to come wandering past, and even mating in them (hence males having such a long metasoma).
So, things to check are temperature, which seems to be ok. Humidity should be low, the substrate bone dry and the enclosure needs to be well ventilated. Water can be provided by spraying a side of the tank and/or providing a small water dish every week or so (more for juveniles, less for adults). They need hides that replicate the rock cracks they'd live in in the wild. A stack of thin rocks, slates or bark with gaps just wider than the scorpion will work well. I've found they much prefer a hide that is off the substrate and one that they can barely squeeze into. Whilst it is fasting I would offer food every 2 weeks, leaving it in overnight and removing it the next day if it's not eaten, so as not to stress the scorpion. A sign that your scorpion may be interested in food again is if it begins to sit at the entrance to a hide with its pedipalps sticking out.
