Trying to write a novel, please critique this sample?

Okay, so I am 15 years old and all my life I've had a love of reading and writing. I'm writing a novel, and would loved to have it critiqued. Don't be too mean, please :) thanks. The sample is the just the introduction to my story, I need to see if my voice and diction are good. So here is the sample.

A woman is on the corner of 67th Street. With her stiletto heels, her Christian Dior gown, and the way she exudes confidence like an aura, she looks like a supermodel. But yet, she looks around, wary, like she is hiding something. Shivering, she puts her gloved hands into her pocket. This is strange. Why is she shivering? It isn’t cold. For Manhattan in February, it is quite warm. I myself am wearing a short sleeved shirt and shorts. I walk to the newspaper machine, slide a quarter into the slot, and get the Sunday edition of the New York Times. I saunter to a bench and pretend to read, while in truth looking at the woman on the corner. She doesn’t notice me. Nobody really does, since I seem to have a knack for invisibility. The supermodel woman looks around furtively, her gaze skipping right over me. Once she thinks she is alone, she opens her expensive looking purse and pulls out a gun. Startled, I almost drop my paper. The woman bursts into tears. Ribbons of mascara trail down her face as she puts the gun to her head. I drop my paper and run to stop her, but I am too late. She pulls the trigger. Her slight frame crumples on the ground as I stand frozen in the rainy, desolate landscape that is the dregs of New York. The color red makes its debut on the gray streets of the city. Her head lay in a pool of scarlet. I close my eyes. All I can see is red...