Hello fellow merfolk! So my parents surprised me with a my first tail for Christmas, a Finfolk fabric tail (the Dark Iris), and when I went for a swim in it, I noticed that it kept slipping down. I measured as a medium, but we didn't realize that sizing down would give for a more appropriate fit (meaning that the next time I want to buy one, I should shoot for a small). Does anyone have any tips when it comes to altering Finfolk fabric tails? My ankles and calves fit perfectly in the water, but from my knees up it slips down and I have to keep pulling it back up. I'd hate to try and do it, only to end up ruining such a gorgeous piece, especially because it is quite an expensive gift, misprint or otherwise.

I would be grateful for any advice anyone has to offer!