I think you're fine, really.
I would avoid using the word 'fanfic', because that implies a derivative work based on something that's currently in copyright, and as you say, you've written a loose retelling.
As far as being up on ff.net goes: this used to be something that publishers would find problematic, but I don't think it's really an issue any more. The bookstores are full of stuff that was previously up on fanfic forums (Fifty Shades of Grey springs to mind), writing communities, or was previously self-published. It certainly wouldn't be a problem for me; increasingly I'd see it as an asset, if there was a ready-made community of fans in place.
I'd tell people that you'd workshopped it with an online writing group, maybe?