Duck-tape on Plastic fluke insert (underwater with duck-tape)

[mermaidsammi]

So my Mother printed me a tail and I hade a thin plastic insert for it so the whole fluke is filled, sorta like a Fin Folk only not at all as good. I have duck taped my Fin Fun monofin into it (I have taped a monofin before) the ducktape holds while I am kicking like a crazy like a fish out of water on my bed, anyone knows if it will hold well enough underwater? I have also added little pieces of duck tape to the corners so it's not sharp.
Praying it will hold or that someone knows a trick!!