This happened to my son when he was 2; see a private dentist if it will make you feel less stressed, but the tooth isn't loose then it probably isn't going to get worse by Monday. I totally understand all your feelings; I felt the same, but it will be alright and it is not your fault!
My son sheared the back of his baby tooth off and this left a point at the front. My dentist wanted to remove both top front teeth because she felt that if a baby tooth was damaged it could stop the adult one growing in straight, as the baby tooth guides in the adult tooth's position. I did not want the teeth taking out so I phoned another dentist.
The second dentist said that the teeth should be left alone; we left the tooth alone and the adult teeth came in straight.
The fall had killed off the tooth at the root though, so the tooth did go grey over time, but it did not decay; the nerve had just died. There was no opportunity for composite because the whole back was sheared off and a composite would not have worked. It may be possible in your case, but I am not a dentist so can't advise.
I would advise: if you are not happy with the first opinion see another dentist.
I know it looks bad and I was initially distraught; however baby teeth are not going to get bigger and your child is, so the visibility of the front tooth in his mouth will reduce over time. Most people will not notice the tooth as your son gets bigger.
I hope this has not worried you more; it seems awful when it happens but it is a baby tooth and so will go eventually. But I cried loads when it happened to my son, so I totally sympathise.