You start low, gracefully curve to the headlights, then from the headlights to the spoiler is a more or less a single, unbroken line that’s slightly angled to make it interesting. At the spoiler you curve upwards, the reverse of the hood, giving a nice “swoosh” through the car. The car is also long and low, leading a thin look. However, if we look at a Fiat 500
We start almost vertical, then there’s a right angel to get to the hood. The line of the hood (what exists) and the implied line across the windows aren’t inline, and there’s no spoiler to balance it off. It’s also short and tall, meaning not thin. This picture cheated with a black line to hide that, but it doesn’t help.
Because of this, the porsche looks sleek and the Fiat doesn’t.
So, in your case, I would determine what major “lines” you want your character to have and build off those. A fairly straight back, and a solid S on the underside will get there. Your boobs are gonna throw that off, but getting the major lines right will help.