Savile Row Garments making

Hello,

I'm working on the 'Prepping for Lining' video and I never made a chalk line to turn back the side of the vent. I remember the 'Reinforcing the Vent' video said that 3" is usually good.

As I have over 3" at the bottom should I trim some of this down or just turn the edge under? Is it 1/2" I need to turn under?

Thanks.