You'r g-code is in inches, and it sounds like you're machine is setup in mm's?

But that shouldn't really matter, as Mach3 will convert the code to mm's.

So, the .063 depth should actually be cutting a 1.6mm deep.

Bottom line, there's nothing wrong with the code, and nothing in it is telling it to plunge seep into your part.

My guess is that something is wrong with your Mach3 setup, or the process you are using.