[Frustrated Gram]

I am repairing some Fuzzi Bumz for my daughter and the elastic is shot in the legs. I have tried to replace it the same way the tutorial shows however, when I sew on the elastic and I stretch it out as I sew it on it does not retract when I'm done. It looks just like the stretched out elastic. Still Shot! What am I doing wrong? Can anyone help me? Frustrated Gram!