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Good afternoon. Getting the card would not help, since you were not legally in possession of the marijuana at the time, so the prosecutor would not likely retroactively say you had legal possession of the marijuana. However, based on the charge, not sure how the State would be able to prove there was an intent to sell, if you simply had half a joint on your person and admitted to it for personal use. Moreover, if the Officer let you go and did not preserve the evidence, there would be no proof. If there is a warrant, you do need to either get it lifted or tun yourself in, for a court date to be set, so you can appear and fight this. If you still know who the detective is, you can reach out and speak with them about cooperating.
If you turned yourself in, you would simply need to bond out and appear at your next court date. Since they did not make an arrest, it does not mean the officer did not document this and take the joint as evidence. Of course, when the case is handled, a demand for discovery could be made and it could be known if he actually kept the joint.