I'm a noob and not even sure of the words to use to describe my problem.

I'm engraving dog tags for my school and the F1 works perfectly when I do one at a time, but I need to make a ton of these so I built a jig from DesignFind. 

Something in my settings is off because the engraving comes out uneven and lighter in spots than the single.

What am I doing wrong?

Is there a name for this phenomenon so I can do more research? 

How do I fix it?

Many thanks for your ideas and advice.