You're already at the very bottom of the weight range for your height. Since Atkins is designed to burn stored body fat, and you probably have very little of it, this probably isn't a feasible way to slim down.

If you really want to lose size without compromising your health, maybe you should try an exercise regimen such as Pilates that is designed to make you look trimmer. Please don't do anything that will endanger your present or future health simply to achieve what you think is a more pleasing look.