What shall I do my uncles threatened me to do everything for him if not he will tell my mom my darkest secret?

This sounds like a stressful situation, one that is not fair on you. Your Uncle does not have the right to control you. Ask yourself if this secret is as dark as you think it is and would it be more harmful for your health to keep the secret rather then your mom finding it out. Is it possible you could have a deep and meaningful conversation and share this secret with your mom explaining your side and how you feel about it. I understand if this is to hard. What would you suggest to a friend if they came to you with the same question?