Just got an mip in michigan not really sure what to think about this?

I was just in a parking lot drinking a beer with a few friends and undercover cops came over asked if i had been drinking i said no then he asked like 2 more times and i was like yeah ok i have been. He wrote me up a ticket that said observed consuming a 12oz bottel of beer. He told me to plead not quilty in court but how can i do that when he wrote on the ticket consumed..? I turn 21 in less that a month and im going to call to make my court date within the next few days. If its going to tbe on my record will it come off once i turn 21? thanks guys if you have anything else to let me know id appreciate it cuz im freaking out