Hi
Sadly Sketchup has a limit of 0.001" when it compares for equality.
When you set the tool diameter to 0.02mm the offsets become 0.01mm
This means that when you try to offset by 0.01mm (0.0003973") Sketchup will consider your new offset points equal to the existing points because they are less than 0.001" different.
I think you can make the drawing say 1mm too small and then use a tool diameter of 2mm. the cutline will then be offset 1mm from what you drew and result will be the correct size. You can even set the diameter to 2.02mm (or whatever needed) to get your final cut size correct.
I would do this by completing my drawing at correct size, then making a copy of it, then at offset lines to the copy (with Sketchups offset tool), then delete the original lines. This way you still have a copy of the original, and adding cutlines is relatively quick.