It's possible his arm is swollen from falling off his basking spot. It does look like a decent drop for the little guy. You might want to try a lower basking site with a higher wattage basking bulb.
What is your basking surface temp at currently? And how are you measuring it?
Swelling in the limbs can also be caused by inadequate calcium absorption, which would be related to you
UVB bulb setup not being too great. I imagine the coil is on the right hand side of the tank, opposite the basking site? The coils produce hardly any UVB at all, and with where his basking site is, he's getting 0 while he basks. If anything, move the coil over to be right beside the basking bulb so that he gets the highest heat and UV in one area. But still, you're going to need to switch out the Coil for the long tube fluorescents.
He is young, so you want to make sure you get this taken care of ASAP before it ends up causing him life long issues.
I'd suggest ordering the items online. They are cheaper than in person typically anyways.
-Brandon