I don't know what the symptoms were before the pics. How long has the Betta been sick? Is he still eating?
Velvet / Oodinium can wipe out an entire tank within a week. I take it your Betta has been sick several days, so unless it's covered with a fine yellow dusting of Oodinium, probably not that.
From the pics, it appears that the Bettas scales are pineconing, possibly Dropsy.
Dropsy is a symptom of an intestinal infection of some sort. By the time Dropsy is observed, the damage is usually done. Survival is doubtful. The best course of action is keep the water very clean, slowly stabilize the temp. To normal levels, 78 degrees, and keep watch. If things get much worse, best to euthanize the Betta.
The best first aid kit for any fish is regular tank maintenance and WC's. Even the most advanced hobbiest has a disease outbreak occassionally, so don't let this get you down. If you want to stock up on meds for future use, Rid Ick has been endorsed by many on this site, for Velvet, I've used Coppersafe.