Discoloration.

My concern is the following:

My apple watch has a discolored semi circle of about 5 milimeters, near the right down corner. I bought this watch at a Best Buy store, about or more than two years, not sure about this but quite some time has passed. Always I treated it carefully, I would say, very carefully. Always I put it screen protector. Never ever I used in humid areas. What are my options...?

Thanks for any information.