Hi indianyogi,
When smoking changa or enhanced leaf, you must use as little heat as possible, and just quickly cherry the bowl and don't apply more flame, take long, slow pulls and hold in for 20 seconds.
How strong is your leaf? A 1:1 ratio of leaf to DMT is good, and if you are not contraindicated then harmalas will make it easier as the time window of administration is longer, it just keeps building up, unlike without harmalas, where you need to get it in you fast.
It sounds like the real issue is with the fear of taking a breakthrough dose, if you stop at one hit, it is likely just not enough to get there. There are many threads to help with breaking through, but it sounds as though your problem is just with comitting to going through with it. Make sure it is a good time to do it, your head is clear and calm and just go for it if everything feels right.
Maybe it's just not the right time.
"If you're not terrified you took too much, you didn't take enough"
Also, "You're never ready" are two McKenna quotes that come to mind.
It is definitely hard to work up the nerve sometimes.
I wish you luck, and I hope you have a wonderful experience on the other side!
AcidShard