Sarahp2222, hi dear, I know you are having a hard time with problems in your bum, is ok to be scare is nothing wrong with that specially when you are facing a surgical procedure for the first time, it can be very stressful.
Rest assure that surgeries are common procedures, the job of the
anesthesiologist is to make sure that your body weight, health and other issues are taking into consideration before your surgery, you will have a prescreening and blood work done to make sure you are healthy enough for surgery.
I had several surgeries under anesthesia in the last 10 years, yes is very scary and on my first one been a major surgery that required 5 days in the hospital I had to ask my doctor for sleeping and anti anxiety pills the week before the surgery.
But once your are under anesthesia you will not remember a thing until the time you are waken up to realized that is over, you will be monitored and taken care.
You have your age as an advantage, been young is a plus.
So let the doctors take care of you and fix the problem and you will be fine.
Remember to come back and let us know how things goes and your recovery progress.
I wish you the best.