How do I make so that the UV Grid is not stretched?

I have 2 objects, 1 plane and 1 rectangle (long cube). I’ve unwrap the 2 (using Smart UV Project) and then created materials (generated type: Empty) for them and tried texture painting them using the same texture. The texture painting for the plane looks ok but for the rectangle, its blurry and seems stretched out.

I tried creating a new material for the rectangle this time using a UV Grid and found out that the grids are stretched:

It seems to me this is the thing that’s causing the blurriness. What do I need to do so that the UV Grid isn’t stretched? The only thing I was able to do is create a material with dimensions 2048x16384 then after that the UV Grid is not stretched anymore. But the problem with this is when I save the image it is very large (and also its slowing my computer when painting).

Have you tried applying the scale on the rectangle?

Hi, yes, its already applied.

scale the long cube islands in the uv editor on either axis until the texture grid is square. The cube has unwrapped as a square so the island uvs are stretched.