If you were cited or arrested for this it is definitely a misdemeanor. Your record can be sealed in most states at 18. from the facts you recite it seems the store is willing to settle this without going through criminal court but I can't tell. If they are willing, pay them and nothing will apppear on your record.
There are a few issues here. First, you will be charged with a misdemeanor. Larceny (which is the category shoplifting falls into) under $250.00 is a misdemeanor in Massachusetts. The maximum sentence for a misdemeanor is 2 and a half years in a county jail. Pretty scary?
That being said, if you have no record, and are willing to pay restitution, there are a few possibilities as to what can happen - and none of them are jail. Depending on the court you are being summonsed into, you can get a diversion program, be ordered to do community service, pay court costs or get probation. You should really consider hiring an attorney to help you navigate the system and protect your record.
First and foremost, you should NOT even think about accepting any disposition that even hints at jail. This is a first offense misdemeanor and you will be looking at some sort of probation at the worst. Probably the most important thing that you can do to influence the outcome is to hire a good attorney. There is a reason why people who are smart and well off tend to do better and that is that they are smart enough and have the means to hire a very good laywer who is not going to settle for a quick and easy resolution. So, if you can afford it, hire a good lawyer. The concept that your record as a minor is sealed when you become an adult is not the case at least in MA. Your record stays with you for life, whether it is as a minor or as an adult. Protect it at all costs. You will not even remember what you did with the money that you saved by going with the court appointd lawyer 2, 5 or 10 years from now. However, your record is with you for life. I assure you that you will kick yourself for many years to come if you cut corners here and pay the price with your CORI (criminal history).