Underage Possession Jurisdiction

My question involves criminal law for the state of: Virginia
I received an underage possession charge in a dorm room, and am representing myself due to extreme financial issues. I only have a question which I would like to ask before I speak to the Commonwealth Attorney. At the time I wasn't in possession of any alcohol; however, it was in the room because my friends were drinking. I don't want to give specifics of my actual case so I will create a hypothetical situation. Say I had a beer in a separate county and after a couple hours I got a ride to my friends room. When the police arrived we were extremely cooperative and the police officers asked if we had been drinking that night, which I had one beer hours earlier. I responded yes and received the ticket. The question I would like to ask is, does the court have a viable case if neither the police officer or Commonwealth Attorney can prove I had broken the law under the Campus Police's limited jurisdiction? Thank you for any feed back. Also, is there any way that my "testimony" could be retracted. I think I have read enough about the Miranda Rights to realize mine were not violated, but figured it was a question I would like to ask.

You don't have to be holding the bottle to be in possession.
Your hypothetical situation will result in a guilty plea. The cops asked if you had been drinking and you said yes and they found alcohol in your room? That's plenty of evidence. There's no jurisdictional problem with the fact that you had been illegally consuming alcohol in some other county. What was said can't be unsaid (and even if it could, I doubt it would make much of a difference).

Miranda only applies to questioning AFTER you are in custody. Police are free to ask questions without warnings prior to arresting you.

Thanks for the information. So being detained in a room does not count as being placed in custody? And even though I was not in possession of any alcohol at the time in any manner, that still can hold up? Even though these may come off as stupid questions I am just trying to help build a decent argument for myself with the help from this forum. Is there any argument to the fact that they had not specified as to what we were drinking, even though alcohol was implied?