Thx both!!
I have corrected the microstepping and testen using the video above.
These are the new grbl settings
$101=39,9429386590585
$101=39,9429386590585
But still, I carved a 50mm square and the X 49.06 and the Y is 49.45. so still not within the accuracy it should be, and it is also not square.
Any more ideas please?