Instead of curvy why not say a voluptuous size 12 and then add height and bust size
Normally on the phone for people who have not seen a photo of me I say I am mid 30s I have a voluptuous, rubensque figure with firm 38g boobs a light tan, long legs a peachy bum and piercing pale green eyes. I dont give a clothes size unless asked as the description I gave is enough for them to know I am not a size 8. Some guys think a 12 is quite slim and others assume it means fat as guys have no idea about womens clothes sizes especially for taller women.
Its not what you say so much as how you say it. say it as if you feel sexy and confident. Never use any remarks that may sound as if you are not as good as the woman on the ad. If she is smaller than you say you have a more peachy bum and firmer larger boobs etc, Never be negative, and never say I am curvier than the picture as that is saying I am not as good. Say the picture is just for the ad and I can assure you I am much better in person and have a rounder more grabable bum and larger firm bust, Always overstate your best points. You have to sell yourself in a few sentences.
If none of that appeals why not just say something like, I am not the person in the picture but I can assure you I am much cuter, I have long soft black/blonde/brunette hair, striking blue/green/brown eyes that I have been told have a wickedly naughty glint, baby soft lightly tanned skin, a firm insert (bust size) bust, and a lovely bouncy yet firm bum.