The fins look jagged like that because the fish is in bad shape. When discus are stressed they often fall victim to intestinal parasites which causes them to starve and waste away. You can see in the first picture that its body is very thin around the forehead and spine/lateral line area, often referred to as "razorback." If you look at the fish head-on, its body will often look "pinched" in right above the eyes. Their fins usually get ragged and their eyes go dull, too.
I would get him eating. If he's not eating, quarantine it, jack the heat up to 90F, and run a metro treatment on him. I've had to do it with tons of discus over the years.
Luckily you only paid $6! I really wish LFS wouldn't sell discus if they don't know how to properly house them.
BTW, it appears to be a turquoise or red turquoise.