Don't use a wait block to try and control Frame Rate accurately. Scratch has a time resolution of 1/30 seconds (hence 30 Frames Per Second) any in-loop wait delay between 0 and 0.03, produces the same result - a 0.033 second frame time (~30 FPS) Any wait between 0.033 and 0.066 produces a 0.066 second frame time (~15 FPS). Any wait between 0.066 and 0.099 produces a 0.099 second frame time (~10 FPS) ... You get the picture. Run the project and experiment with different wait delays to see the result.
See inside.