If you had a week left I would've suggested to spam hours at a library or something, but looks like you don't. You could always get someone to fake a sig but that could get you into more trouble and not really worth bc it's a fucking underage alc charge ffs. Never procrastinate with legal shit bro: taxes, fines, and shit like this because it will catch up to you, and now you got yourself a charge on your record. RIP STEELO