@Themaster154,
Lots of us have thoughts that we never act on - even dark ones. That's okay; it's just your imagination. One way you can channel that is by writing. Even if you don't think you're that good, writing can be a good way to get that stuff out. If you don't want it to be found, you can always erase any electronic documents or discard, shred, or burn any paper ones.
If it is really bothering you, you can talk to your mother again, but this time in the context of asking to see your doctor and maybe getting a referral to a therapist. It doesn't mean you're violent, crazy, stupid, autistic, or anything else! It just means you would like to talk to someone about it, someone who's a professional. That's all.
It's gonna be okay.