Are you not able to log in on the story side with the username and password you used to post that story? If you do have that login info, the easiest way to find your piece is to go here, log in, then navigate to see your previous submission(s).
Otherwise, what username did you post it under? What was the title of the story? Which category was it in?
Either the author or title should allow you to find it easily. For instance, you could google:
site:literotica.com your_author_username
and/or
site:literotica.com "your_story's_title"
(put the quotes around it and add the category onto the end if you know it)
Alternately, you could try the search function on the story side of Lit. I often find Google is quicker when I'm looking for specific things, but you should be able to bring up anything written by your own author's name easily via the story search.
It shouldn't be hard to find as long as it wasn't removed for some reason. Occasionally, pieces that violate the rules are posted in error originally, then removed when someone reports them later on, but that's not a common occurrence because the story editors are very good about catching problems in the first place; it is FAR more common for pieces to be deleted from the site at the request of their authors (not an issue here, since you're the author).
Do your best to search for it, and if you can't find it, post all of the pertinent info so one of us can help you look.