Only cardio is not a key! If you want to have a nice shape of your body you have to weight train or at least bodyweight train.
Lets take this example: Fat woman who looks like a big plump starts training aerobics only, after a year she have lost 40 pounds, but she still looks like a plump except smaller. She has no shape! Why? Because she only did cardiovascular exercises.
Weight training or bodyweight training tone your muscles, defines a nice shape. Doing only cardio means loosing muscle tissue and body fat at the same time, so you will loose weight, but still look without curves. I would recommend doing cardio 3-4 times per week of 20-30 minutes session and 3 times per week weight/bodyweight training.
Besides that, you have to control your meal plan. 5-6 small meals during a day keep your metabolism rates high and in this way you burn more calories. Every meal should include complex carbs and protein. I am going to make a hub about good diet soon.
I hope my answer solved your problem. Feel free to ask again.