Internal crack on the back plate

Bought the watch 4 weeks ago, 2 weeks I was in quarantine after returning to Korea, so barely touched the watch. When the quarantine was finally over, I took out my watch to go running. As I was putting it on my wrist I saw a crack on the sensor area(back plate). Never dropped or hit the watch in anyway... had it for less than 4 weeks(2weeks in quarantine without using it)...can't even feel the crack with my finger nails(internally cracked)...no bumps or nicks that shows that I could have dropped or hit the watch...Apple won't fix it for me... wants me to pay $500 to repair a $800 product...What do I do... so bummed about this...