How to make my chin slimmer?

You could define the sides of your chin with a bronzer or a dark brown eyeshadow. It will make your chin look more slim and defined. Then once you brush it on blend it so there are no harsh marks. Youtube videos about contouring which excally what you want to do. Contouring your face can bring out hidden line and creases in your face which can make your cheekbones look more defined. You can look up ways to contour your face shape. I cannot see your entire face but i think you have a diamond or a square face shape. :) your chin look great though! it looks very portioned to the rest of your half of your face lol :)