If i fail my first drug test for juvenile probation in CA, what will happen?

I am going to be drug tested in 2 hrs, and i am going to test possitive for THC. I plan on just telling my probation officer that I'm dirty and ask for a chance. This will be my second time meeting with my PO. I got probation for theft. I want to know whats most likely going to happen after meeting with my PO.