Looks like you started from a cube and did not layout the UV's. Follow Dave's instructions and select the object and then go to create UV's and select automatic. As he said that will correct the stretching although you may get seams.
You could also select create UVs > planar projection options and pick best plane. This should give you a seamless projection of the UVs for the floor plane.
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675