How to make bullet spread in 3D top-down shooting game?

I am trying to make a shotgun script, but the bullet only spread if the character is facing the z-axis and it gets more concentrated as it turns to face the x-axis.

I already looked at some of the similar questions in the community but most of them are FPS game and coded differently. Does anyone have any idea how to fix this?

Here is my code:

 float x = Random.Range(-spread, spread);
 float y = Random.Range(-spread, spread);
 float z = Random.Range(-spread, spread);

 //Calculate Direction with the spread
 Vector3 direction = attackPoint.forward + new Vector3 (x, y, z);

 bulletPrefab.GetComponent<PrefabBullet>().setShootDirection(direction);
 bulletPrefab.GetComponent<PrefabBullet>().setBulletSpeed(bulletspeed);
 Instantiate(bulletPrefab, attackPoint.position, attackPoint.rotation);

The bulletPrefab only have one line of code in the start function:

 public float bulletspeed;
 public Rigidbody rb;
 public Vector3 dir;
 public void setBulletSpeed(float BulletSpeed)
 {
     bulletspeed = BulletSpeed;
 }
 public void setShootDirection(Vector3 Shootdir)
 {
     dir = Shootdir;
 }
 void Start()
 {
     rb.velocity = dir * bulletspeed;
 }