Question about hair follicle testing...PLEASE, PLEASE HELP IM FREAKING OUT!

Hello all,
This is my first post on this site so I hope that I dont sound like too much of a noob but here it goes...
I was offered a job that requires a hair test by the dreaded psychemedics lab. I quit smoking cold turkey 18 days before I was offered the job and when I was finally offered it I freaked out and shaved my head clean as well as the rest of my body hoping the company would offer me the chance to just take a urine test but no such luck. They told me to refrain from shaving my head, let it grow to 1 inch, and then come back and and retake it. I smoked pretty much everyday, 2-3 bowls, for 5 years so I know my toxin levels were pretty high. The 18 days before I shaved my head I worked out alot, heavy cardio on the stair master and lifted weights although this has always been part of my routine as I do like to work out. I figured I'd try and get as much toxin out as I could. I have conflicting reports all over the internet that it takes anywhere from 3-5 to 7-14 days for clean hair to start growing out that is thc metabolite free. So I guess my questions are after I went clean for 18 days, worked out a ton, and shaved my head will the hair grow back clean??? Also does working out release thc metabolites into the blood and therefore into the hair follicle??? I literally cannot sleep over thinking about this as this job will really change my life for the better. Any constructive help would be greatly, greatly appreciated. Thank you everyone!