There has been a few threads about this, and if you add your THC containing matter to the beer, you aren't going to get much THC in the final drink.
The easiest, cheapest and fasted way to do it is by making a tincture, the higher the ABV the better.
THC and most cannaboids aren't water soluble, and they need either lipids (which you don't want in your beer) or high abv to be brought over and activated for consumption.
Depending on where you live, I would find either everclear or other overproof alcohol and soak some greens in it for 3-6 weeks (look up Green Dragon recipies) .
Then add this tincture either to bottling bucket, secondary or the individual bottles.
Best of luck if you try again, and be ready for being hit by a freight train.