Creality CR-10, Z axis issues..

This cube is 20.25 in X and Y axis. 18mm in Z axis. Seems like the clogged bottom part is the missing 2 mm in Z. Supposed to be 20x20x20. Any ideas? Sometimes there is more "clog" and more height missing. Cant get this to work what so ever...

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recalibrate. Looks like you're just too close to the bed for the first few layers.

To calibrate this I used a paper folded in half, should i be even further away from the bed? First printer and my knowledge about this slim to zero..