I wouldn't worry about it too much. Your competition is probably obscure enough that most people reading your story wouldn't have heard of the other. Now, if you're writing about some fearful hero seeking to destroy an object of power while dark beings on horses chase him—you might have more to worry about (but even if you do write such, the story can still have value, and some people are sure to like it).
I recommend doing it anyway, and not caring about thunder. It's good to have multiple slants on the same idea. People might prefer your method to the other, but if you don't put it out there, you might never know.
People are notorious for coming up with wild ideas. I don't think it's that your idea was pathetically easy to come up with so much as there are a lot of writers in this world. Well, whether or not it's easy to come up with you should know the same thing happens with many ideas that are quite difficult to come up with. Don't fret about it too much. I'm sure you'll have original ideas here and there, but I wouldn't expect any of them to stay that way forever. That's the thing about ideas—they are not created or made; they've always existed and always will (every last one of them), unless the way the universe works changes somehow (and I don't mean the way humans perceive the universe). We just realize them, but that can still have significance, caring about an idea because we're close enough to it to realize it.
Anyway, those are my current thoughts.
