Mac pro Retina,some part of the screen coat is lost

I recently found there're some spot on the screen. At first I thought it was dirt, but after that I noticed the screen coat is lost... I clean my screen just using glasses cleaning cloth and water (no chemical product!!) I asked the supporter in apple store, they said warranty is not covered, but its too expensive to change the screen and I dk why it is not in the warranty because I did nothing wrong according to the agreement... What should I do 😟