You can go to that site and search for user "mushtang". I have 598 finds, and 594 on unique caches. So that means I posted 4 finds on caches that I'd already found.
Clicking the link beside those numbers will show you exactly which ones I'd found more than once.
If you've got a MyFinds PQ, you can use the site to figure out which one you posted twice on, and then you can go delete the extra find if you want to.
That site isn't up any more. Is there another one I can use???