Thoughts are not as harmless as they are often portrayed in popular culture.
By this I don't mean that one can just kill others with thoughts. But if there is a close bond between two people (such as often between siblings, or between a mother and her child) then because of this bond, thoughts (and words) have much more power, constructive and destructive.
That said, based on what you said so far, I don't think you killed you mother. But harboring hateful thoughts toward her is bad, it was bad for her, and it is bad for you.
As for what you can do, is reflect on how valuable parents are and what debt children owe them. This is not a popular topic in modern culture, but it is of vital importance for being civilized.