metric to inches scaling issues will have you off by a factor of 25x.
First. go to Config menu, and select "Select Native Units".
If it's not mm, then change it to mm, and close and restart mach3.
Next, go to the setting page and see if it's in inches or mm's.
If it's in inches, go to the MDO page, and hit the "enter" key on the keyboard, and then type "G21", and hit enter again.
Then close and restart Mach3.
Then jog the machine and see if it's moving the correct amount. If not, your steps/unit are wrong.
Make sure that you're using a metric post from Sheetcam, and that there is no G20 in your g-code.