With the size of this cyst, chances are pretty good that it will not resolve on its own. It's good your gynecologist is removing just the cyst and leaving your ovary. Removal of even one ovary can impair fertility and also negatively impact health in the long-term since the ovaries produce hormones our whole lives (yes, LONG after menopause) which are critical to every aspect of health. The uterus also has LIFE LONG functions - anatomical, skeletal, hormonal, and sexual.
I hope all goes well!
You may consider waiting a month and having them check the size again, but it sounds like once they become 5 cm or larger, there is less chance of them going away. I have 3 cysts that they will be removing Wed. (I'm 53 so they're doing a hysterectomy because I requested it since I don't plan on having any more children, etc.).
You don't want your cyst to get too large that you risk losing an ovary at your age. Although, you can still get pregnant with only one ovary. Talk with your mother and other adult females in your life to get advice and make an informed decision that you feel comfortable living with. If you don't like the doctor/surgeon, then discuss with your parents about getting a second opinion.
I get that you are scared. You could get as second opinion before you have surgery. Sometimes doctors watch cysts. The doctor may know that this is a cyst that will not go away on its own. Laprascopic surgery is much easier. Before I have surgery and I have had a lot I try not to think about it. It is easy to think of all kinds of scary unknowns. I have had 19 surgeries and nothing went wrong with any of the surgeries. The main thing is to trust your doctor. If you do not find another doctor that makes you feel safe in there hands. The psychological part of surgery is real. I try to think of something I like. For me it is riding horses. I go through my whole ritual in the barn in my mind when I get nervous about surgery. You can't think of two things at once so no worry.
Alex