Hard for me to tell what that could be from. It could be a small burn, a cricket bite, an injury from rubbing against something sharp, etc. So let’s try to cover them all. Raise your basking light a few inches above your screen top. Babies love walking upside down and have no idea that they’re getting burned. 85 is just a bit too warm for such a youngster anyhow. 80 is ideal for at least a few more months. Make sure that all uneaten crickets are removed from his enclosure and just in case, leave a small piece of produce on the bottom for any stray crickets to eat instead of going after your beautiful boy. Look thru all of the edges, ends and anything else that could have a pokey end. Finally, you want to keep the area clean and can apply the tiniest dot of neosporin (the plain kind that does not have pain relief in it) to help it heal.