If you are putting sand, it likely will flow out under the bottom rails where there will be a sizable gap.
What type of liner are you using?
If you are using something else like extruded polystyrene foam (what I did) then if it is an overlap then it should work fine. If j-hook or bead, make sure you install it on a warm sunny day so it has a chance to stretch into the deep cavity, since the manufacturer is expecting at least 2in of sand inside the pool.
Under the liner will be the manufacturers tarp, and also another heavy duty tarp to cut to the size of the pool. The manufacturer does not suggest the use of sand, this is just a ProSeries pop-up pool 20X48. The actual pool itself is "the liner" with a metal frame.