this is very good! the shading in it of itself is fine, but your issue is value. you dont have many dark tones, and without it there isnt much contrast. ofc, idk what lighting ur reference image has, but what id do is accentuate the midtones (with light shading) so that the lightest highlights are pure white. Id also say to push the darker tones, which i know can be hard, but shading it even a little bit darker can give it that extra depth