Here is how you do it, Make a template for the size you need, Line up the front of the template with the front hairline of the piece
then cut off the excess lace, Diagram below :
What do you use to cut the lace, scissors or knife? Do you leave the template in place when cutting or do you use a marker to mark the lace around the template, remove the template, then cut?
I line the template on the piece, mark out the edge with a marker, and cut along the line with a fresh razor blade from a utility knife just using the point of the blade on the underside of the lace, never had a problem doing it this way.. I cut away the marker line.....