PF

i got an underage possesion in va, im 17 & they didn't take a BAC-- only said they had witnesses that I admitted to drinking.
but when the cop was questioning me i was in the ER with a closed head injury (+alot of other serious injuries) and i dont remember talking to him. i dont remember anything of that evening after i was put on an IV in the ambulance.
it was my friend driving her car & wrecked us & it was her beer (which i wasnt drinking) & her vodka, mixed with mountain dew--which i had so small an amount way earlier that day, that i think i would have passed a BAC had they given one. im not sure how i got a possesion charge, based on solely admitting to drinking (which i dont remember doing)?

can i plead innocent and get out of this?

i know ill only get 6 months suspended and maybe some ASAP + community service if found guilty but how would i go about pleading not guilty?