Hi, I'm On Felony Probation, And For The First Time

Hi, I'm on felony probation, and for the first time since 2012, I had a relapse. Over the course of a week or so, I used probably .75 g of heroin, didn't do it for 3 days then found that I'd forgotten about .1G on Monday and couldn't bring myself to throw it out. I know that's my own fault, that I shouldn't have allowed myself to fall into that situation. After I did the remaining .1g, I got a call saying that my probation appointment was moved to Thursday morning because I'm getting a new officer. I have no guarantee that I'll be drug tested, but if I am, what are the chances that I'll pass? I'm debating telling my officer about it, but that is a moral dilemma for another time. Thank you for your time.