I checked that it never allowed me to change the units lower than mm.

But it worked when i started the new document. it doesn't allow you to change the value on the fly i guess.

this fixed the problem. 

but on a separate note i was also able to fix the problem without changing the units, if i make those vertical lines with the script and still have mm as units i can trim off the outer sector without shifting the center.

anyway changing the units of the document is a much better and cleaner solution.

thank you