(Total amount of dmt)/(total amount of material) gives you the dmt concentration.
500/2650=0.1886
divide by 2650 or whatever the final dry weight comes out to
If you want to know how much dmt in X mg changa. Simply multiply X by 0.1886
For 100mg it'll be (100 mg)×0.1886=18.86 mg
I agree with void that it is a bit low, you generally want to try to smoke as little as possible to make it more comfortable. Unless you are planning to do very low doses so you are diluting the dmt on purpose. You can always mix it with more pure leaf if you want to make a joint or something. I'd also go heavier on the harmalas.
Good luck and enjoy
"Is this the end of our adventure? Nothing has an end. We came in search of the secret of immortality, to be like gods, and here we are... mortals, more human than ever. If we have not obtained immortality, at least we have obtained reality. We began in a fairytale and we came to life! But is this life reality? We are images, dreams, photographs. We must not stay here! Prisoners! We shall break the illusion. This is Maya. Goodbye to the holy mountain. Real life awaits us." ~ Alejandro Jodorowsky