Printing problems

The nozzle keeps hitting the platform when make leveling.

Check the needle which was above the Z-axis limit switch is in the right position. 

Here is an operation video for your analysis. https://drive.google.com/file/d/1oO8pY_bIgPLCEGgM7YEZva-Hpx3mKfCH/view?usp=sharing 

Or you can print a tool add on the Z limit rod. https://www.thingiverse.com/thing:5193360