IPN Evaluation

I recently finished nursing school and passed boards. I found out the day I took boards that my application for licensure was up for review because I had a positive pre-employment drug screen for marijuana. I have had to appear before the BON and they will give me a license but I must first go through an IPN evaluation. I have never smoked marijuana. I tried to contest the results but was told "there's no point, we won't change anything". I went to my doctor and paid to have drug screens done and they all came back negative. My doctor said there are things that can cause a false positive, such as Advil, riboflavin... both I had taken. My question is "How do I get through this IPN evaluation"? I feel like no matter what I say they are going to acuse me of being a drug addict, and make me sign a contract. If this happens I will never get a job as a nurse. I am devistated by all of this and feel my career as a nurse is over before it even got started. I'd appreciate any information on what to expect during this evaluation. I have heard horror stories about IPN.