Yupp that is some BAD bloat, if it is bloat at all! I have seen alot of bloated bettas on these forums, but that one is definitely the worst. It makes me think internal infection-- like some organ inside is jammed up and filled with fluid. Maracyn 2 would clear it up in that case.
On another note, you really should invest in a QT tank... nothing fancy, even a rubbermaid bin will do as long as it has a heater. A heater is a HUGE necessity in treating tropical fish, IMO.
EDIT: Not sure what you mean by Mardel, but if this thing is bacterial, the bacteria are most likely immune to it by now, rendering it ineffective.