Is my career ruined before it began?

I am so scared that I have ruined my future career as a nurse before it has had a chance to begin. I recently graduated with a BSN and I am looking for a job. I passed the NCLEX on my first attempt, which I am very excited about. My problem is that while in my last semester of school, I took Adderall on few occasions to help me study. I do NOT have a perscription for it. A close friend and fellow student who DID have a perscription gave it to me to help me study. I recently found out that all of the hospitals around here HAIR drug testing for pre employment screenings. I am not a drug user, so I beg of you not to make accusations against me. I have put everything into getting thru school. I have 3 children that are counting on me. What I need to know is how far back does the pre employment hair test go back. I know it can go back as long as your hair is, but what do hospitals normally do? It has been about 4 1/2 months since the last time. Any and all help is GREATLY appreciated. Thank you!