MJ is stored in fat so it takes 3-4 weeks to get out of your system but will still be in your hair. The good thing is that you should be fine. That was about 3 weeks ago and being only once in like 6 months will help you out too. Drink plenty of water, oj, and other juices. flush your system out. If you get really worried, just go to GNC or another local vitamin shop and get a "flush kit". usually like 80 bucks but work great. Just don;t tell them you need to get one for a drug test. Its like saying the "B" word in a head shop.