You MUST use one source.
You may use twenty, if you like.
You must have both a thesis that is overarching and tells me the direction you plan to go. Not just “‘Goldilocks and the Three Bears’ shows the flexibility of humanity.” Instead something like “‘Goldilocks and the Three Bears’ shows the flexibility of humanity through the different porridge temperatures, different chair sizes, and different bed hardness. In addition, it shows that even stubborn humans can learn.” Can you see where I could tell what your main points are in the second, but not so much in the first? (Don’t think this would work for 1,500 words, but it might get you started.)
You must use one fairy tale.
You may use two fairy tales (or more), two different versions of the same fairy tale, two fairy tales that are of the same folkloric type (use the Folktexts site at pitt.edu for that), or even a fairy tale and its movie adaptation. You may also add scholarly research or background information that is found at a deeper level than a simple web search or Wikipedia.
You may quote. You must quote at least once.
You may not quote more than 15% of the paper. At least 85% of the paper should be your own thoughts or your paraphrasing or summarizing of someone else’s thoughts.