Typically this doesn't happen often with this recipe since we are using the jello, but if somehow you ended up with runny jam, there is something you can do. You can try to thicken the jam by boiling it in a saucepan. Bring the jam to a vigorous boil and stir constantly until it thickens, usually about 5-10 minutes. You can also add a tablespoon of cornstarch dissolved in 1 tablespoon of water for each cup of jam and then bring it to a boil. This will help the jam thicken up more quickly. If the jam is still too thin even after boiling, you can place it in shallow dishes and refrigerate it until it reaches the desired consistency. But again, this is typically not a problem with this specific recipe.