Nice little story! For the limitation I found you a little shy, like I know what you wanted to do with it, but you didn't commit enough to my opinion. I would've love to see EVERY moving sentences to follow the "don't" logic until the very end. Maybe by adding a voice in the head of the mer princess? ""don't eat more" said the voice in her head -> but the little mer princess ate more" something like this, until she broke free!
I also had the text issue, I fixed it by zooming on the browser to 200%. I suspect it has something to do with monitor sizes, the bigger your screen is, the more zoomed out the background will be (so it will have to duplicate itself to still fill the screen), while the text will always center the web page.
Nice work on the sound design, and the backgrounds were pretty too! It was overall really really atmospheric, the ambiance was well done. gg!