I have never heard of it being tested through hair. Have heard it stays in your hair but seldom is that used as it is so expensive.
You did not break the law.
To say it impairs your judgment days after is not true.
Don't make a habit of it and you will be fine.
Once you get a job don't do it even once.
You can get tested at work, I have, on the airbridge, breath into this and also can I swipe this on your forehead.
It really is not worth it.
I used to smoke it sometimes at school, got tested 2 weeks after smoking and was clear, I guess because I only did it once every couple of months. Would never even think of touching the stuff now.