ricochet bounce effect issue

First of all im really new to unity and programming, soo expect a loot of noob mistakes :)

Hi , im trying to make a 2D game where the bullet bounces off the walls like a ricochet . I got to the point where i can shoot it to the direction im pointing with the ,, gun '' the way i wanted it , then i attached a RAY to it, pointing towards direction its going to . Now im stuck at the bounce effect , i trying to use the Vector3.reflect but its not bouncing the way i would expect it to bounce .It bounces off almost randomly and sometimes its going though the box colliders . I created a 3d box colliders in the places where the walls are , because i found out that rays don't detect 2d colliders or something like that? . I would like to know if the mistake is in my code or the scene design . I will appreciate every help,tip and criticism :) thanks

This is the code
void Update () {

     Vector3 fwd = transform.TransformDirection(Vector3.up);
     //Debug.DrawRay(raycastObject.transform.position, fwd * raySize, Color.green);

     RaycastHit hit;
     Ray ray = new Ray (transform.position , fwd * raySize ) ;
     Debug.DrawRay (transform.position, fwd * raySize); 

     if (Physics.Raycast (ray , out hit, raySize  )) {
         Debug.Log ("Bouce test 1 ");

                     if (hit.collider.tag == "Wall") {
                             Debug.Log ("Bounce test 2 ");

                             Vector3 reflectDir = Vector3.Reflect (ray.direction , hit.normal);
                             float rot =  Mathf.Atan2 (reflectDir.y, reflectDir.x) * Mathf.Rad2Deg;
                             transform.eulerAngles = new Vector3 (0, 0, rot);

                 }

Also this is the bit im using for movement of the bullet

             Vector3 pos = transform.position; 
             Vector3 velocity = new Vector3 (0, speed * Time.deltaTime, 0); 
             pos += transform.rotation * velocity;
             transform.position = pos;