Did he throw the fight?

I would assume that he didn't. In the end he's thinking back to what everyone told him. He finds out that everyone is betting on him. Surprisingly he finds out that even his girl is betting on him. This movie is also a remake of Body and Soul so I say no. He won the fight.

Being that they didn't took him to fight in another country which is not enforced heavily as it is here in the US by the Athletic State Commission, and that they didn't have him go partying with Japanese hookers while getting drunk of Saki, and they they didn't hook him up with incompetent corner men who could not provide a ends well, I would say that no he did not throw the fight, considering he did not do any of those things and he was not willing to let his peoples down.