Hog Island Boa: Stuck Shed, Nose Rub, Or Something else?

[Fire Jets]

Hello! I've noticed that my hog island boa has a brown spot on her nose. I'm a little worried. I am not sure if it is a stuck shed, a nose rub, or anything else? It is quite possible that it is a nose rub, because her cage is a little too small (a 20 gallon [I'm currently building her a new cage, however]). The spot appeared in just a few days...So, what I'm asking is, what the heck is it?! Also, what can I do about it?

Besides the brown spot, she looks healthy and is eating/pooping normally. I've had her for almost two years, and her behavior has not changed since the brown spot came.

Her temp is roughly 87-ish. I don't know the exact humidity percentage (the thing I have is junk), but her sheds have been good (except for a couple; but I aimed to increase the humidity).