Don't the words "insertion scale" provide any clue? That is in reference to units to scale inserted content and does not refer to lines you are drawing.
Did you use the wrong template (metric instead of imperial or vice-versa)?
Stick with one or the other don't try to combine the two or you'll just cause yourself all kinds of grief. If you are comfortable working in metric units but the client wants to see imperial units then address the problem using the Alternate Units feature of your Dimension Style.
If you've progressed too far to turn back then you'll have to resort to scaling the drawing up or down depending on what units you started working with.