As an MP myself, I can tell you GO TALK TO LEGAL THE OFFICE if you haven't already. Its their job to look out for you, regardless of what youve done.
Its all going to be dependent on what youve said so far. The USMC has a zero tolerance policy on drugs, yes that includes AAS. However, you havent tested positive for anything have you? Until you do they have zero proof you have done any of the gear, you were just holding it for someone