normally i'd say, wtf ja??? don't do that shit, are you crazy!??????? (rhetorical question, i know)

but this kinda stuck out.. "I really do care what this chef thinks because hes been good to me and did a really good job of conveying his ideas. Also he said that he would be happy to let me practice my knife cuts in his class. (hes not supposed to do this really)"

I think you should do it. Going from a C to a B doesn't seem too important, though. In the food/bar industry, experience and people skills get you a lot farther than grades. In a roundabout way then, this suggests you should do it.