Is there anyway to fix a stretched decal on a part? If so is there a script

As far as I'm aware there is no way to stop a decal stretching. If you'd prefer for an image to repeat across a part, use textures instead.

umm well i made a mesh and i decided to put a texture on it, and for some reason the texture was very very stretched, so if there's a way to fix it please tell me

I beleive you stop the stretching by using surface gui's