So, why do you pre cut the boo to shape?
I have a pattern that is the exact shape of the bow I want.
Or I could layout a bow pattern just like you glass bow guy's do.
After rough flattening the belly side of the boo, I lay the pattern on the flat side and trace it out. Then cut to that line, then thin and taper the boo thickness to what I want. Can you imagine trying to draw a pattern on the round back side of the boo?
Then after the bow is all glued up, all I need to do is cut along the edge of the boo pattern and there is my bow.