Possible B Felony For MDMA

My question involves criminal law for the state of: Oregon

I was involved in an incident in my dorm room where Campus Public Safety found a single tab of ecstasy in my room. At first they thought it was my girlfriends & I wasn't there so she was booked and charged with possession of a controlled substance for the mdma along with a charge for delivery of marajuana which is entirely her deal. Apparently she told the police the ecstasy was mine, and Campus Safety had me come in and talk to them today. They said that they weren't going to file charges although it would be a B felony because it is a schedule 1 controlled substance, instead they would leave it up to the District Attorney whether or not to file charges. I guess my question is, how likely is that? This is my first ever offense and I haven't even technically been booked or charged with anything yet. I'm supposed to be leaving in a week to study abroad for a month.

We have no idea how likely it is that you will be charged or not.