The stretchy sheet of space time illustration is just a simplified visualization space is 3 dimensional so the warping is 3D. The stretchy sheet visual is used

The stretchy sheet of space time illustration is just a simplified visualization space is 3 dimensional so the warping is 3D. The stretchy sheet visual is used a lot because showing a warped 3D grid to be more accurate is a lot harder and a lot less clear and illustrative. Trying to show a 3D grid doesn't even fully capture the situation because it doesn't show how the passage of time gets distorted as well.