I did the math and saw how on your resolution, the tops of the balls were starting above the top of the screen. I tried the same again for 4096×2160 (4K) and 30px isn't enough for that.
So, I've updated it instead to use midtop (https://gitlab.com/neilsimp1/double-down/-/commit/62c81010a66c52e100adcc23b1c4e7...). I believe this should work for any screen size now.
I've updated to a 1.0.1 release here, https://gitlab.com/neilsimp1/double-down/-/tags/1.0.1 but I am not sure if it's ok to update what I have submitted to the game jam or not, so I guess I will leave that be for now?