If you’re feeling unsure, spend more time thinking about it - seek out a therapist who specializes in gender identity. One of the great thing about transitioning is it’s your transition - nobody can tell you when to do it, how to do it, or anything like that. Your journey is your journey, so if you are feeling unsure just take the steps you are comfortable with. Start by seeking out a therapist, that is the best way in my opinion to talk through any hesitations, insecurities, or uncertainties that come up along the way.
As far as your Mom - all do respect to her, she isn’t you, she doesn’t know how you feel inside in regards to who you are. Her response could be one of denial, shock, or any number of emotions that parents go through when their children come out as trans. Hell, my father blamed the internet - it was all the internet’s fault. I went through a lot with my parents until they finally found acceptance with it. You can read more about my detailed experience with family through the links on my FAQ Page. Though this was her initial response, it doesn’t mean it is her final response. She could very much just be in shock or denial (like most parents tend to be when their children first come out) so remember her reaction can change. Leave the dialogue open, give her some time - while it is a huge transition for us, it’s also a huge transition for our families and loved ones. So, my best advice would be to just give her time, and keep the dialogue open.
Hope that helps some!
Whitherward keychain, final version. Look for these at Denimbruin and online shortly after.