I Took A Drug Screen And I Used Magnum Synthetic

I took a drug screen and I used magnum synthetic urine. I put a 8 mg diladid in the sample but when I saw the dr he said it show I had taken diladid and oxocodone. there is no way that oxycodone could have been in the sample as I only put didalid in the sample. why is this, and also they are sending it to the lab and I would like to know if the magnum synethic will show up as fake