I'll approach this from a different angle than the two great answers already here. Let's assume that yes, your story is too similar to an existing, fairly well-known property. How do you fix that?
1) Address the root cause. Figure out the story you're trying to tell, and how your similar aspects tell that story. Do you like the idea of balancing pairs of forces? The idea that nature exists in sets of four? Playing with the four ancient elements? Figure out what part appeals to you — get down to the nub of the thing. Could you instead use the Four Humours? The four winds? Name your power aspects after the four suits in a deck of cards? (and not everyone uses the same deck. French and American decks are hearts/diamonds/clubs/spades, Italian and Spanish decks are cups/coins/cudgels/swords, Swiss-German decks are roses/bells/acorns/shields.) Invent your own suits from an in-universe deck and have the characters use the suits as nicknames for the powers? Use Tarot cards with major and minor houses?
2) Rework the problem symptoms. If your problem is that you have four Powers, and one person has All Four Powers, well, why? What's the story you're trying to tell about this person? Does it have to be one person with all four powers? Could you have a gang of four or a Five-Person Band (WARNING: TV TROPES LINK) working in tandem? Could the powers be in artifacts and the character has to collect a series of MacGuffins instead of having innate abilities?
This can obviously be altered to fit whatever your specific issues are. My point is, if your reader radar is redlining into Fanfic, and you don't want to write fanfic, you need to find the heart of your story first and then work outward from that. If your story is so closely bound up with the original property that you can't separate it, then go ahead and write the fanfic, or the pastiche. The writing will be practice and you can tell some other story once this one is out of your system.