As I just had this happen... XD I was spelling "armour" as "armor" and somebody commented about it, so I started using British spellings. BUT, I don't think it's entirely necessary. I do tend to preface with a warning for American spellings, though, just so people won't think I'm an idiot who can't type. *she says as she accidentally types "idoit"*

As far as the story goes, I'd say keep going. If somehow it turns out that your story is like, exactly the same (highly unlikely), you may consider scrapping it, but a similar premise (even a very similar one) isn't automatic grounds for people screaming "plagiarism OMG!!". (Plus, y'know, so far, Merlin fandom is freakishly awesome and full of cool people who do not seem crazy. *is loving this* *is also assuming fandom-in-question*)