Unity Random Range doesn't work as expected

I programmed a little pong clone. At the start, the ball spawns in the middle of the field.

Expected output: I want the ball to fly in 45 degree angles to the upper right and left, and lower right and left randomly.

Real output: The ball only flies to the upper right and lower left.

Code:

public class BallController : MonoBehaviour {

public float speed;
private Rigidbody2D rb2d;
private int counter;

void Start() {
    rb2d = GetComponent<Rigidbody2D> ();
    SetStartPosition();
}


public void SetStartPosition() {
    this.transform.position = new Vector3 (395f, 295f, 0f);
    int xVector = GetRandom ();
    int yVector = GetRandom ();
    float x = (float) xVector;
    float y = (float) yVector;
    Vector2 movement = new Vector2 (x, y);
    rb2d.velocity = movement * speed;
}

private int GetRandom() {
    int i = 0;
    do {
        Random.InitState((int) System.DateTime.Now.Ticks);
        i = Random.Range (-1, 2);
    } while (i == 0);
    return i;
}

}