There could be a few reasons why the jelly is runny, from not squeezing out all the liquids or cooking it long enough so that the water couldn’t evaporate to not using enough or the correct pectin. It’s also important to make sure you are using the right amount of sugar and making sure the cans have properly sealed while canning them. If the jelly is runny and not setting, you can always use it as a sauce, glaze, or marinade instead.