Welcome to the Nexus!
Spirituality and psychedelic drugs can def be very transformative. I find that another essential part of that equation is to also have healthy habits, like vigorous exercise, good nutrition, sleep.
If you feel your negative past still affects you, maybe finding someone who can help dealing with the psychological struggles can be good too. It could be a professional help, or maybe just someone who you trust and that can give you good feedback and a different perspective to your issues.
Regarding your dark entity experience, if you haven't read yet, check
this and
this out. I find that often the darkness we see outside is just a reflection of some inner conflict we are dealing with inside, and once we can raise ourselves into a new level of personal development consciousness, that darkness dissapears, stops being a problem or directly becomes our ally, like the Medusa's head being used as a weapon, or all the "taming the wild animal" analogies/images in alchemy. Jung's work on the integration of the shadow is very interesting.
Im not sure if every single entity is just a reflection of ourselves, who knows, there may be independent entities in unexplored dimensions or any
infinite number of hypothesis of what reality is, but either way I feel that ultimately we are part of Everything, like a particle of God in a sea of Love, so there's nothing to really fear. Entities cannot touch our divinity, and for that we can be stronger than any challenge. Or at least that's what I have told myself and worked well during some very difficult experiences.
Have you also considered oral DMT instead? I find it lends itself better for personal development, though some vaped DMT exploration can be positive too in some moments.