Need help with a problem (I don't know how else to put it)

The most frustrating thing about writing my story is that sometimes when I think I get a new idea for it, it turns out they're parallel to ANOTHER story I've been following, an RPG group. The worst part is, I don't know if it's just a coincidence or if I did it without meaning to. I'd think, "Man, this is a really good idea! Glad I thought of it." Then I'd realize I HADN'T thought of it, and be forced to scrap the whole thing.
Other times, I DO think of a really cool idea, then I'd go browse the group and read something that sounds like it, and then I won't be able to use my idea lest someone think I was copying if the story ever gets published. I just don't want another "The Lion King vs. Kimba the White Lion" incident (that nearly ruined the movie for me). I also just want my own, original storyline.

I'll take any advice you guys have to offer.

I understand what you're feeling.
I've consulted others on this website, and most of the time, it's over thinking on my part.
If it's a simple plot point that shares similarities to an already existing story, and certain elements aren't exactly the same.

One thing I learned a few months ago was that no plot is actually original. You have the same basic themes throughout all of literature. You'll follow the hero's journey, and some high school english class will point out the call to adventure, the climax, all that fun stuff.
Really, we're all writing things that we can compare to other books. Just this morning I was browsing the library, and one book was described as "a cross between the Selection and Reign."
Books are like other books. Stories are stories.
To make something your own, you need to just do it. Write it. Your story will parallel someone else's. But you can't twist it and make it your own if you stop writing it and scrap your ideas before they're fully baked.
For example, I'm writing a novel based on Alice in Wonderland. Obviously it's based on Carroll's original, and then there are a million other AiW retellings and fanfic type books. How is mine going to be different?
….I'm working on it lol. I could explain the whole plot, but that's long.
BASICALLY THOUGH you just need to write it, realizing that your story will probably follow the templates that all stories follow, and you just need to have original characters and a good enough shuffle of plot devices and few enough tropes to make it great and original enough that no one thinks "gosh this is exactly like book x that I just read."
"To steal ideas from one person is plagiarism; to steal from many is research." So steal from many writers and spin all those ideas into something that's your own.