How about looking into some legal protection? Even a terminally ill dying girl can refuse a surgery if that's not the person wants to go through, you can not be forced or coerced to have the plastic surgery if that is not your wish. Defying parents is a part of growing up, a mark of a thinking man, it's best to come up with your own reasonings of why you should be able to wear short sleeves, and not everyone think bad of you because of the scars. You know your own progress and you will get wiser and stronger, you may still need a lot of support from your parents, but there's one thing that all of you can not do away with is the trust, in you. Are your parents gonna be the part of the solutions? I hope you can stand your own ground.