Relax and just fly your bird. It´s been said that only a small fraction of P3 may develop cracks, most are OK. Keep an eye out on the shell, and as a rule on every other part of your P3 - that´s nothing out of ordinary, should be standard procedure just as it is with general RC aircrafts and other hobby models. Good luck and happy flying!
A small fraction is more than enough to be concerned when people have spent so much on these things.
I would not advise anyone to ignore cracks for many reasons.
Either get it replaced by the dealer or see what DJI say. If it's a p4 I would be sending it back to the dealer for a replacement.. Cracks should not keep happening like this.