To ledge dash break it down into multiple steps. Start by making sure you can let go of ledge and DJ towards stage on frame 1 of leaving ledge. Most of the time you airdodge offstage and die it is because you were trying to be optimal but pressed jump too late. You have to make sure you have the jump timing down first. Then, once you are good at that add the stick angle to ledgedash and the airdodge input. Ultimately you want to be good enough at each ledgedash step to feel in your hands what part you did wrong when you put it all together. If you manage to master perfect ledgedashing (hard btw) then you can casually add the turnaround uptilt.
On a side note the ledgedash has another key factor that is overlooked or underrated in it's difficulty, which is timing when to start it. You have to be ready to grab the ledge or you might jump the gun, and then tournament winner because you hit away from ledge before it was possible. It's kind of like acting OOS with hard tech, sure the tech is hard but so is timing when to start it. So if you find that you are landing the regular ledgedashes but missing them in real games, it means you should probably practice them alone after real recovery options; jump offstage and sweetspot up b from different angles, mangle into sweetspot, side-b, even shortening. It really helps to practice recovery options and ledgedashes together.