Strange screen issue on my Apple Watch Series 5

I've bought an Apple Watch Series 5 a few months ago and haven't used it much since. A few days ago I picked it up, because I wanted to use it again and there is a strange screen issue now. I have never dropped it and it was laying around on a desk for the time I didn't use it. I'm also almost a 100% sure it wasnt there before. It looks like one area of the screen is darker than the rest. Even if i try to remove it with my finger or a tissue it just doesn't come off. The screen still feels like one plain layer. I'd like to know if this is an issue which the apple repair covers. Thank you in advance.