You will probably receive a civil demand letter from the store asking for damages between $50-$500. The letter will threaten a possible civil suit if you don't pay. Whether or not you pay will have no impact on the criminal prosecution. The payment of the fine cannot be used against you at any subsequent criminal action.
If the store decides to tell the police and the police decide to seek a criminal complaint against you, you will receive a summons in the mail to appear for a clerk-magistrate's hearing. At this hearing, the clerk will decide if there is probable cause to issue the complaint against you. The clerk's hearing is an excellent opportunity to resolve the matter without a criminal complaint issuing and I strongly recommend that you have an attorney at the clerk's hearing. If the complaint issue, you will be scheduled for an arraignment. The arraignment date is also another opportunity for your lawyer to resolve the case without generating an entry on your record. If you are arraigned, the charge will appear on your record, regardless of how it is ultimately resolved.
There are long term consequences, even if you have no prior record and are only 21. My advice is to consult with a criminal defense attorney and maximize your chances of minimizing any damage this criminal act could have on your future. Best of luck!
If Marshalls files a criminal complaint it will go on your permanent record, unless you can get it dismissed prior to arraignment, which is never easy. If you are criminally charged, hire a good defense attorney if you can afford it. You may think you shouldn't bother because it is a misdemeanor and only a fine, but the truth is if it is a criminal complaint and you don't know what you are doing, it will most likely end up on your criminal history (CORI). So, if your future chances of getting a good job and/or going to school and getting financial aid are important to you, do not take the charge lightly. I don't think anyone should ever go into court without an attorney. You only have one chance to get this right. Don't blwo it. Look on here and look at all the questions that people have about trying to change an outcome after many years have passed. They consistently say the same thing, I should have listened to my attorney or I diddn't think it was serious at the time, etc. But they are all kicking their own buts now, wishing that they had taken it seriously way back when they had the chance. NOW is your chance. Get a good lawyer. The money you save today you will not even remember 10 years from now when you are kicking your own butt because you didn't handle this right when you could.