Your first step is to recognize that you are in serious trouble and you are facing at least two criminal charges - possession of a forged instrument in the third degree and unlawful possession of alcohol. The first offense, possession of a forged instrument in the third degee, is defined as: "A person commits the crime of criminal possession of a forged instrument in the third degree if he possesses or utters a forged instrument of a kind covered in Section 13A-9-4 with knowledge that it is forged and with intent to defraud."
Your use of a false or forged "fake ID" to falsely claim to be at least 21 years of age in order to make an unlawful purchase of alcohol is clearly within the terms of this offense and your use of the "fake ID" implicates this offense. Possession of a forged instrument in the third degree is a Class A misdemeanor and punishable by a fine of up to $6000 and a sentence of up to 12 months incarceration (limited to six months incarceration if the court having jurisdiction is a municipal court). Additionally, it is probable that this offense constitutes a crime of "moral turpitude" in that it involves falsity, dishonesty, and false statement or act.
If the "fake ID" as a false Alabama driver license or identification card, there is another, but similar statute, found in the Code of Alabama at section 13A-10-14: "It is unlawful for anyone to possess and present a facsimile of an official identification card issued by the Department of Public Safety." That offense is also a Class A misdemeanor. Note that mere possession of a false state-issued driver license or ID is a crime unto itself, without the need to use the false instrument.
In addition, the possession, purchase, transportation, or consumption of alcoholic beverage in any form by any person under age 21 is a unscheduled misdemeanor offense, and punished by a fine of up to $500. See, Code of Alabama, 1975, section 28-3A-25. In addition, if convicted, to include the application for Youthful Offender status, the Department of Public Safety is required to suspend the driver license and/or driving privilege for a period of not less than 90 days of any person convicted of that offense.
Your best course of action is to seek the professional services of a qualified criminal defense attorney, and especially an attorney who specializes in alcohol-related offenses and crimes. For a listing of criminal defense attorneys in your area, check the listings for the Alabama Criminal Defense Lawyers Assocation at: www.acdla.org. You may wish to check the listings on Avvo of criminal defense lawyers who specialize in DUI and alcohol-related offenses. In any event, you should recognize the seriousness of the offenses and possible punishments.