if its working OK other than the parts are too big with mach 3's default settings
how big is the error in size ?
you will need to set up mach 3 as in the mach 3 manual
in mach 3
the units may be set up incorrectly what units are you working in ?
eg mach set in inches instead of mm would make parts 25.4 times too big
if Ucancam is set to mm
then you need to check the steps per unit
the pitch of your lead screws may not be the default pitch
John