You have differing forces working against you. Attempting to make the bend at the crease of a crowned panel is pushing the ends of the crease back outward to form more of a straight line, losing some of your crown. You can't make the entire bend without shrinking along the way. With your FSP on the original piece, you should be able to mark where this crease is located. Now transfer that mark to the new patch. Just as we're bending something across a sharp anvil here:
You'll need to do similar. But since your panel has a crown, your "anvil" should not be straight across, you need to have the ends relieved/radius-ed to match the panel's crown.
So my anvil could look like the last pic, with maybe a tighter radius
Next, we bent the flange in the video in three or four steps. Note when bending the radius toward either end of the tail pan, we start to have ruffles or tucks forming as this excess metal is trying to go somewhere. This is why you can't form the complete bend all at once. Slight bend from one end of the crease to the other, then shrink as needed to restore "crown" of the main part of your patch. Here a profile gauge would be handy in addition to the FSP.
I have plenty of these profile gauges made to help me just in case. see pics below
Once crown is back where it should be, slight bend again from one end to the other, shrink again as needed. Repeat as needed.
So I need either a shrinker stretcher or I need to make tucking pliers from vise grips like you did?
As to marking where your crease goes, I prefer to mark on the top side where you will be hitting with the hammer. If your crease gets slightly off the mark, you can immediately see it. Readjust, hammer to bring crease back to the mark, and continue.