iPhone 11 with smudge on screen.

Ive taken out an iPhone 11 on contract about 3 weeks ago , so it’s basically brand new. I’ve noticed a smudge on my screen that won’t go away no matter how much I wipe my screen. I started googling around and came to the conclusion that it could either be water damage ( which isn’t the case because the phone hasn’t left my sight and I take good care of it) and I’ve checked inside my sim tray if the LCI is white which means no water damage and it is white. What could the problem be ?