Iniquitous would mean that it is unfair, and therefore wrong on a moral level. An iniquitous system for instance would be a system that gives a certain individual or group an extreme advantage over others. The example you gave wouldn't work, because it would imply that your class was getting this exercise in order to disadvantage you, which I doubt. Even if that was the case I would refrain from using this word, because it implies a systemic unfairness, rather than a single exercise, or even a single teacher being unfair.
I hope this cleared it up.