CNC Y-axis error

Hello guys,
i am exceptionaly asking for help, i have a little issue with my CNC, i am using a 7i76e Mesa running 3 axis, i experience a dimensional error in my Y-axis. I have 3 linear scales, the Y-axis has a linear of 5um resolution and a closed loop stepper motor attached to a 1605 ballscrew (16mm width, 5mm pitch), so my problem is that i have an "accurate" innacuracy that means my axis undershoot exactly 0,1mm in other words it mills 19,9mm instead of 20mm or 299,9mm instead of 300mm and so on... i dont know how to fix it without using Backlash = 0,1 because my ballscew has no backlash on the dial gauge. Does anyone has a simple solution on how to add 0,1mm to the .HAL file?
Thank you very much guys !

Is it -0.01 on internal shapes and +0.01 on external? Or the other way round? Or neither?

Thank you for your response Andypugh!
Saying that the target is a D10mm boring, it becomes D9.90 mm, if it is D10mm outer round shape it becomes D9.90mm (only in Y) X Axis is in both shapes D10mm

Do the glass scales say that the axis is in the right place?

This is very hard to explain.

Yes they do say that they are in the right place

If i just could say to the machine net y-pos-cmd => pid.y.command + 0.1 it would be perfect but unfortunaly it's not that easy to add 0.1mm

hadcom wrote: If i just could say to the machine net y-pos-cmd => pid.y.command + 0.1 it would be perfect but unfortunaly it's not that easy to add 0.1mm

Actually, it is very easy to add 0.1mm. But that would just move the whole part 0.1mm.

Does the Y PID have any deadband set?

[AXIS_Y]
MAX_VELOCITY = 116.666666667
MAX_ACCELERATION = 750.0
MIN_LIMIT = -0.01
MAX_LIMIT = 450

[JOINT_1]
TYPE = LINEAR
HOME = 0.0
FERROR = 10.0
MIN_FERROR = 1.0
MAX_VELOCITY = 116.666666667
MAX_ACCELERATION = 750.0
# The values below should be 25% larger than MAX_VELOCITY and MAX_ACCELERATION
# If using BACKLASH compensation STEPGEN_MAXACCEL should be 100% larger.
STEPGEN_MAXVEL = 156.25
STEPGEN_MAXACCEL = 937.5
P = 50
I = 0
D = 0.001
FF0 = 0
FF1 = 1
FF2 = 0.00073
BIAS = 0
DEADBAND = 0.001

And yes that is what i need, if i put in CAM a square with dimensions X 10 and Y 10.1mm i get Exactly 10x10mm and that also true for any dimensions like X500 and Y500.1mm i get Exactly 500mm in X and Y there is like missing 0.1mm but i dont know how to program it..

You could try setting the deadband in the INI to zero. But I doubt that is it.