Rays with this type of injury usually carry on life as normal.
You have been very lucky, if the hole had been the other side of that birth mark it would have been all over. This type of injury to the abdomen is usually fatal, however it has simply punctured the cartilage of the gill chamber, it will heal quickly(usually less than a week) don't worry. If your water parameters are good then it should heal well without the need for medication, I would personally just add 1\2 oz per gallon of salt to help with the healing process.
Keep us informed.
All the best!
Ps
I agree with the guys, its a puncture wound from a spine (stinger)