It may vary where you are located but reading the standard warranty provisions for an Apple Watch it is not covered by warranty for scratches and cosmetic damage. If you have taken out Apple Care etc it may be different. I have not checked that out.
Here is the relevant part of the warranty as it applies to the USA, taken from this link http://www.apple.com/legal/warranty/prod...
WHAT IS NOT COVERED BY THIS WARRANTY?
.......................This Warranty does not apply: (a) to consumable parts, such as batteries or protective coatings that are designed to diminish over time, unless failure has occurred due to a defect in materials or workmanship; (b) to cosmetic damage, including but not limited to scratches, dents and broken plastic on ports unless failure has occurred due to a defect in materials or workmanship; .......................
You may wish to check for where you are. Select Apple Watch, then select your location. http://www.apple.com/legal/warranty/
I must be getting old, I'm envious of your eyesight for even noticing it.