I told my mom about it but she said I dare better not say anything
What is the reason why your mom is threatening you to not say anything?
I fear what happens if I don't say anything to her
I feel like she's being very threatening and I do not think it's the right behavior for a mother making you fearful about being honest, and I do hope you get a different family member to deal what you have been dealing with and get your mother to be more accepting and less threatening in the process.
I know, but what I am saying to her is not that important.
If you still need to say it to your mother, no matter how big or small it is, then you still should tell her. It is very unhealthy to keep something from someone and you will feel relieved by being honest and truthful no matter who you say it to, not just your mother.