All the water of Earth, condensed to a single sphere.
You make several assumptions. One is that the land masses were the same and of the same height. But that’s a digression,the earth’s land masses were completely covered in ice at one time so...
By faith, we believe the Scriptures. Permitting that point of view to “filter” what we see, the world is one big kaleidoscope of evidence for the (one) worldwide flood.
For example, try explaining the formations in the Western US desert any other (credible) way.
If you will not believe, then I cannot persuade you, of course.
Is that accurate? That doesn’t seem like enough. I guess from our perspective the oceans seem really deep but in the scale of the whole globe they are just a thin sheet. Still seems like too little, though. And by the way, that sphere is sitting right on top of my house.