Make sure that when you melt the marshmallows that you use the same amount of marshmallows by weight. Since the marshmallow creme in jars are whipped up a bit to make it fluffier. Usually a jar of marshmallow creme is 7 ounces, so use just a little bit more marshmallows by weight. Or you can make your own marshmallow creme. There are a few recipes here on this site. But, its just easier to just melt marshmallows.