First, Welcome to the forums.


If I understand correctly, your plan was to leave the backing larger than the batting and front then fold it over to act as binding but while cutting you have cut into the part of the backing you need to fold over as binding?

Hard to say without seeing the damage but I would say cut the backing flush and use a separate binding. It is very difficult to repair cut fabric.

Sorry your scissors messed up your hard work. My wife and I have both done similar things with scissors and a rotary cutter to projects we were working on. I guess it is all part of being a quilter.