Help Battery overheating, possible screen damage

Had my XE for 3 months and it only really heats a lot when playing games.

The hottest part being the bottom of the screen and over the buttons.

After reading online that it's common I haven't been too concerned, until today.

I was sitting doing some browsing on my phone in a fairly bright spot and noticed a small triangular shaped mark on the backup button. My initial thought was it was just a bit of grime, so, I cleaned it, then, upon closer inspection it appears to be under the screen.

It's pretty faint but i'm concerned that the excessive heat in that area of the phone is starting to warp or burn the under layer of the screen.

I can't seem to find any other examples of this online and was thinking of contacting HTC if it worsens.