Scale rot? Dehydrated? Ball python help!

[SoSo]

My four month spider ball Python lives in a 20inch tank enclosure. The hot side is in the 80s, while the cold side is in the 70s. I try my best to keep the cold side on the low-mid 70s, and the hot side in the mid 80s. It generally works but since I have heat lamps, the humidity goes down fast. I try to get it to 50, but most days it's 30-40. I then turn off the heating lamp, spray some water, and then wait till the humidity goes up before turning the lamp back on which takes a good five to ten minutes(im just assuming I never actually timed it- it could be way less). He just ate three days ago and before that he ate four days ago. He is fairly skinny to where his body is more triangular than round & his spine shows. He's not severely skinny but he could use some fattening up. He spends most of his day hiding. His first/last shed was a month and a half ago. It went fairly well. My issue now is that the scales on his shed appear to be as if may be in shed. They look a bit... Bubbly? I wouldn't know how to describe it. I was wondering if it may be something serious where I should go to the vet, because he may be dehydrated, or perhaps because he is skinny? Or if he may have rubbed his spine against something. I put a branch for him to go in that he spends most of his time in and he just loves it. It is fairly small and a little rough inside (not majorly just like if you got wood from outside), so could that be it?

[SoSo]

http://imgur.com/a/my4nG

[dr del]

He looks fine.

He may have rubbed it a bit or the very top layer of the scales may have come off with his last shed.

[SoSo]

Oh thank you!!!

[amozo]

I think your temps are too low. His cold side should be around 80 and hot side at 90.