If you were ordered by the court to take parenting classes and you haven't enrolled, I suppose the worst that could happen is that you would be found in contempt of the order.
However, if you have proof of your attempts to enroll, and proof that you are indigent, I doubt that will happen. What is more likely to happen is that another hearing date will be set for you to provide proof of enrollment.
I suggest you look into other parenting class programs that are court-approved programs, and ask about fee waivers or reduced rates or payment plans.
Although a court can order you to take parenting classes, the court cannot expect you to take classes when none are available for you to take or that are financially impossible for you to afford.
Good luck.