Shud i be scared to tell my mom that i believe in god?

no, you need to tell her. she might be mad for a while but she needs to accept that thats who you are.
the opposite thing happened to me, my mom is catholic and i told her i was atheist. at first she was freaked out and got mad, but accepted it and we now get a long really well. we just dont talk about religion.
just tell your mom you believe in god, dont tell her that she's wrong for not believing and your right, just let her know where you stand
hope this helped and good luck! just do what feels right, belief is a big part of who people are and you shouldnt hide that