I am making a space shooter but my bullets keep on going up instead of out and not deleting from the Unity Hierarchy

I am trying to practice making a space shooter in order to build on concepts for my main project, and I am having issues because I have gotten where the bullets fire and follow with the ship but they fire up and never delete from the hierarchy in Unity.

Here is the code for the Controller:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerController : MonoBehaviour
{
    private Transform myTransform;

    public int playerSpeed = 5;
    // Start is called before the first frame update
    
    // Reusable Prefab

    public GameObject BulletPrefab;
    void Start()
    {
        myTransform = transform;
        // Spawning Point
        // Position x = -3, y  = -3, z = -1
        myTransform.position = new Vector3(-3, -3, -1);
    }

    // Update is called once per frame
    void Update()
    {
        // Movement (left / right) and speed
        myTransform.Translate(Vector3.right * playerSpeed * Input.GetAxis("Horizontal") * Time.deltaTime);
        
        // Make the player wrap. If the player is at x = -10
        // then it should appear at x = 10 etc.
        // If it is positioned at 10, then it wraps to -10

        if (myTransform.position.x > 10)
        {
            myTransform.position = new Vector3(-10, myTransform.position.y, myTransform.position.z);
        }
        
        else if (myTransform.position.x < -10)
        {
            myTransform.position = new Vector3(10, myTransform.position.y, myTransform.position.z);
        }
        
        // Space to fire!
        // If the player presses space, the ship shoots.
        if (Input.GetKeyDown(KeyCode.Space))
        {
            // Set position of the prefab
            Vector3 position = new Vector3(myTransform.position.x, myTransform.position.y - 2, myTransform.position.z);
            
            // Fire!
            Instantiate(BulletPrefab, position, Quaternion.identity);
        }
        
    }
}

and here is the one for the Bullet prefab:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Bullet : MonoBehaviour
{
    public int mySpeed = 50;
    private Transform myTransform;
    // Start is called before the first frame update
    void Start()
    {
        myTransform = transform;
    }

    // Update is called once per frame
    void Update()
    {
        // Shooting animation
        myTransform.Translate(Vector3.up * mySpeed * Time.deltaTime);

        if (myTransform.position.z > 20)
        {
            DestroyObject(gameObject);
        }
    }
}

Not sure what I am doing. The bullet has gravity unchecked & is kinematic checked.

Player is positioned at -3, -1, -3.