If you got a lot of blood when you cut, you cut too early. Like ruf said, wait for the first to pip. Cutting early is not the end of the world however you run the chance of the liquid egg contents going bad. If this happens the snake needs to come out whether it is ready or not. If you run into this, PM me and I will explain what you need to do which is basically build an artificial egg that can house the animal in the incubator until the yolk sack is absorbed.
I always remove my animals once they are out of the egg. It is easier to keep track of who is who.