I’m wondering how to come out to my mother and I’m pretty sure that she will be fine with it but I’m terrified that she won’t accept me, what should I do ?(I’m bisexual)

Is your mom homophobic or ignorant? Because if it’s ignorance there is a chance she will learn to accept.

Just bring up “how do you feel about lgbt” in a conversation and hear what she says, and correct her misconceptions. Then you can ask how she would feel if she knew you were bi, depending on how she takes those misconceptions.