ok firstly, you need to get with a modeling agency. how tall are you, because most models at 13 are already 5'8 or taller, and for VS, that is basically a requirement. if you're not that tall, or even close to it right now, then chances are you will not grow to the required height, and therefore cannot be a VS model. there are no VS models under 5'8. none whatsoever.
secondly, if you fit those requirements, then you need the correct measurements. the standard model size is 34 chest, 24 waist, and 34 hips. if you dont have that, then get to it, but only if you're the right height. to get your chest measurement, measure around the fullest part of your chest. your waist is about an inch above your navel, where your body naturally has an hourglass shape. your hips, contrary to popular belief are around the fullest part of your butt.
thirdly, you need to be in the market, which is basically New York City, and you need to be repped by one of the most reputable agencies, like Ford models, Elite models, or IMG models. (Miranda Kerr, Giselle, and Heidi Klum are with IMG).
IF you fit those requirements, then you have a very slim chance of becoming a VS model. Be warned, it is NOT easy whatsoever. Most of the VS models have a big name in the fashion industry already, and are chosen by VS themselves.
Honestly, you'd be best to focus on something else. Hope this helps.