(Forgive me for still using inches)
No! 
You may partly be forgiven, though, since many/most printer/driver manufacturers seem to favour the Imperial way of thinking.
A few questions:
- What printer?
- Do you have CUPS installed?
- What paper size?
- Do you set your margins in darktable, or in Turboprint — or perhaps in both?
- Any scaling set in dt, or in Turboprint — or perhaps in both?
Have fun!
Claes in Lund, Sweden