Can't really tell what you have it sitting on. Plate corals want to be on the sand bed because of how much their tissue will expand. If it's elsewhere, the tissue could get damaged or irritated from the constant expansion/contraction cycles. But I wouldn't think that would happen in one day.
More likely, it was either damaged during transport or handling between the LFS
and your tank... assuming it was OK to start with. If it was fully expanded at the store, you probably wouldn't have seen those areas where the skeleton is sticking through the tissue. (I assume we're talking about those areas at 12, 10, and 7 oclock?)
Not much you can do with it except give it some TLC and small bits of mysis a couple times a week. You don't want too much flow, but if you notice any tissue sloughing off it in those areas you should probably blast it away with a turkey baster.