Being interested in Satanism doesn't have anything to do with being possessed. So knock that off the list. If you're interested in Satanism, then follow that path. If that's what floats your boat, then let it float.
Anger issues and "feeling powerful" aren't due to being possessed either, so you can knock that off the list, too. Meditation can calm your anger, or doing something that expresses your feelings, such as writing, drawing, or painting.
It's a possibility to have some kind of entity attached to you.Or some sort of negative spirit. Why do you think you got it from your uncle? I think anger issues and certain hyperbolic emotions can be due to genetics. Is your uncle normally an angry person?
One way that you can deal with negative energies, however, is to cleanse your home, space, property, and rooms. You can do this by simple visualization and meditation (this goes for cleansing yourself and your room), and you can burn sage. It is a protective and cleansing herb, and is most commonly used to cleanse homes. You can also use cedar (healing and purification), rosemary (if burned, can be used to ward off negativity), or Angelica root (protects against negative energy and attracts positive energy; creates a barrier against negative energy).