How can I make a scalloped overlay (fondant on fondant) so that the scallops are even and don't distort when transferring to the cake?

It's a bit tricky.
I cut the fondant scalloped circle on a flexible plastic mat.
Then you lift up the mat and flip it upside down. The thin layer of fondant will stick to the mat.
You lay it exactly where you want it and then allow the fondant to roll off of the mat as you hold the plastic egdes taught

It's like how they use that commercial product called "The Mat" except I don't use 2 plastic sheets