I was given the Movie Nite oil popcorn maker as a gift and it says that it makes 12 cups of popcorn but I am only getting 4 cups. Do I need to buy a special type of popcorn? Can you put more that one scoop of kernels in the kettle at one time? Please let me know what I am doing wrong. The flavour is great on the popcorn that I do get but I would like to be able to make more at a time.