I'm sorry that you didn't realize that double chins weren't Gyaru. You are totally missing that trend.
You see, double chins have been a trend for the past 10 years in the Gal community. It makes your face look fuller and give you that perfect oval face shape that everyone wants. The best way to accentuate your double chin is to high light it with a really bright and shiny white makeup. That way when you go in to Shibuya 109, all the non double chin Gals will get super jealous of you.
Have a good day.