Need to set position z to 0

I am making a achievement system to save all my achievements when unlock and show which achievements is not.When I try instantiate a prefab, the z position is making my prefab look small and out of place. I need to set my position z to 0 using c# code. At the moment when I instantiate a prefab the z position value is 1557.057 and making the prefab look small in my panel.

code for instantiating the prefabs in my panel

using UnityEngine;
using System.Collections;

public class AchievementManager : MonoBehaviour {

public GameObject achievementPrefab;

// Use this for initialization
void Start () 
{
    CreateAchievement("Streak");
    CreateAchievement("Streak");
    CreateAchievement("Streak");
}

public void CreateAchievement(string category)
{
    GameObject achievement = (GameObject)Instantiate(achievementPrefab);
    SetAchievementInfo(category, achievement);   
}

public void SetAchievementInfo(string category , GameObject achievement)
{
    achievement.transform.SetParent(GameObject.Find(category).transform);
    achievement.transform.localScale = new Vector3(1, 1, 1);
}

}

Try this:

    Vector3 position = new Vector3(transform.position.x,transform.position.y,0);
    GameObject achievement = (GameObject)Instantiate(achievementPrefab,position, Quaternion.identity);