Man, I think this has happened to most creators! My personal favourite is when I had this story idea I was very excited about, about a digital world where corrupted characters are called "glitches" and basically shunned and treated like terrifying vampires, and then exactly two days after fleshing out this concept I saw Wreck-It Ralph in theatres and spent half the movie just screaming internally. xD
I didn't change it, though, and a week later I was laughing about it. I considered changing things, like whether it would be better to use a different word for the glitches, and finally shrugged because even if I develop this story as fast as I possibly can, Wreck-It Ralph will be years out of date by the time I'm ready to share it.
There were things I thought about tweaking when I saw how similarly they'd been done in .hack//sign, another story about a digital world, though, since that one is a bit more of an enduring example of the genre. Not major thematic things -- I'm keeping those -- but little things that I thought might be distractingly similar details.
For me stuff like this isn't so much an issue of "will someone think I stole it" / "did someone else do this first," but more a consideration of "will the similarity be distracting for the people reading my story." I've always felt strongly about this --
There’s a few other similarities too. So…. yeah, okay! I started telling people “it’s kinda like .hack//sign, where they’re all in a MMORPG, except…” and embraced the similarity – if you liked what .hack did, maybe you’d be interested to see what this story does. I think it’s okay for stories to kind of come from the same place, the same concept, and then branch out to touch different themes.
-- creating something that's really similar to something that already exists is okay to do!