It's ok to not have all the answers straight away, figuring out your sexuality is usually a process that happens over time, and is not usually set in stone. It's totally valid to identify as Questioning
in the meantime if that feels right to you. If you're deciding if bisexual is a good fit as an identifier, you might like to read through this advice column: How do I find out if I'm bi or not?
Does anything in that ring true for you?
In terms of who you speak to and when, you know your mom best so I'm not going to tell you exactly what to do. If you like, you could start by laying a bit of groundwork by bringing up LGBTQ+ things that aren't about you, so you both get a chance to get comfortable speaking about these things together, and you might get a sense of what information you want to go to her with and when. Questions you can ask yourself are things like what do you want from these conversations with your mom? Do you want to speak to her about the process of questioning, or prefer to come to her with something you feel pretty confident in?