You need to reference your enrollment agreement and any other contracts you have with the college. If these agreements state that, under the circumstances and timing that exist, you can't drop the class, then you can't drop it--such a term in a contract is enforceable. On the other hand, if you may properly drop the class under the terms of your enrollment, then you can do so--and if the college will not you, you'd have good grounds to sue them (such as in small claims court) for any money you lose due to their refusal.