I am on the seed worstseedever and at coordinates x: 315, y: 12, and z:-92. I have a 20x20x3 room around that point and am on normal difficulty. The area is also lit up with light sources no further than three blocks from another light source. However, even waiting about 30-40 blocks away the slimes still are not spawning. So is this the correct area for slimes or am I doing something wrong.
Pearl fc: 0430 5356 0434 FFCC: Echoes of Time fc: 1977 8801 1268
It shouldnt matter what height you are at, as long as you are closer to bedrock.
However keep in mind the person posted the coordinates of the center of his room, which may not actually be a slime chunk. Your room is smaller than his, meaning you may not be in a chunk that spawns them to begin with. He never mentioned the coordinates where he saw one slime spawn, just where his GIANT room is. I also think you said your room is 20x20x3 ? If so raise the ceiling to 5 or 6 blocks.
Either way, extend your room a little bit. Slimes also have a very small chance of spawning. If there are any enemies around (behind the walls of your room) in the same chunk, slimes may not spawn. Hence the need for a such a large room.