Insurance Drug Test- I am being drug tested for life insurance and need some help?

I am a 16 year old kid and my parents are getting life insurance for themselves. I will receive the benefits should anything happen but I was just informed that I too will be drug tested for this. I have a numerical 4.0 GPA and it is expected of me by my parents to go to a good college but at times I vaporize marijuana or consume it through tea or food and also take adderall which I am not prescribed for. My first question is why am I being drug tested if that doesn't affect the liability that my parents are to the company and also, what happens if both of those show up positive? The last time I consumed THC would be 4 weeks before the drug test and the adderall would be 8 days. what should I do? I do not want to let my parents down as they would be devastated.