Gotta Take a Hair test! Thinking of going Jerry G. Any Advice?

Im gonna have to give a hair sample sometime in the next couple of weeks and I have a question about J.G method. I have thin hair and am not sure if I should go w/ the 40 peroxide. I dont want it all to fall out!! Has anybody had success w/ 20 or 30%? I am a heavy Dabber(Vape pen and Honeycomb Hash)but havent been smoking for a couple of days. Do I have to do the bleach twice? Also plan on getting some Ultra Kleen. Does that stuff even work?