Concentrate on the good feelings and thoughts you had. Let all those bad thoughts fall to the side. Try and not ruminate about it. You have been given a choice. Two experiences. One good. One not so good. Which will you concentrate on more?
You may or may not receive the kind of experience you are after. I think eventually if you do DMT enough times you experience an all over the board thing, just seems to be no ryhme or reason to it at times. Then one day, three months later a thought pops into your mind and something clicks in your mind and thinking. You can learn from any experience you have.
Don't have any expectations and do your best to free your mind of worry before the trip. Chill out and relax for a few minutes before. Ground yourself and think of what you want to get out of these experiences.
Weed could affect the DMT trip. I think anything you have in your system can play a part in how the experience unfolds. Although I wouldn't go blaming the weed right off the bat.
"In the universe there is an immeasurable, indescribable force which shamans call intent, and absolutely everything that exists in the entire cosmos is attached to intent by a connecting link." ~Carlos Castaneda