Nice shape for the headstock! I think we're using the same mat.
I only have experience with transfers in scale modelling, but I'm pretty sure the priciples are similar - clear coats to conceal the line of the decal's edge. In my experience it's likely that when you're done, you, the builder, are going to be able to find a way to angle it just right, with the light in the right spot, and looking at it from just the right angle, that you'll see the outline of the decal, but it's unlikely that anyone else will ever notice.