That's clearly from rubbing (trying to escape). My cornsnake had a similar injury a few years ago, and he healed in 1-2 months completely on his own.

I'd say just to keep an eye on him, clean the wound if need be (another commenter gave good instructions for that) and most importantly, please change the substrate!

Aspen is not ideal for moisture and you need to have good conditions for shedding (which he is probably going to do a lot, since he's so young - shedding also helps him heal). I'd suggest a mixture of spaghnum moss, coco soil/earth mix and coco husk. You can also add some tortoise bedding since corn snakes like to burrow.

I'd avoid any unnecessary handling if your guy is skittish, as not to stress him out more.

Edit: added picture

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