Tiles spawn on top of eachother

Hi,

I've been trying to create a endless runner type of game as my first project.

Right now my script generates a path using tiles, it adds tiles and removes them from the back. Id like to make the tiles random, so that I can add different obstacles to them. I created two prefab tiles but they seem to spawn on top of eachother and I don't know what's wrong with the script.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class TileManager : MonoBehaviour {
6.  
7. public GameObject[] tilePrefabs;
8.  
9. private Transform playerTransform;
10. private float spawnZ = -5.6f;
11. private float tileLength = 5.0f;
12. private float safeZone = 30.0f;
13. private int amnTilesOnScreen = 7;
14. private int lastPrefabIndex = 0;
15.  
16. private List<GameObject> activeTiles;
17.  
18.  
19. // Use this for initialization
20. private void Start () {
21.  
22.   activeTiles = new List<GameObject>();
23.   playerTransform = GameObject.FindGameObjectWithTag ("Player").transform ;
24.  
25.   for (int i = 0; i < amnTilesOnScreen; i++) {
26.  
27.    if (i < 2) {
28.     SpawnTile (0);
29.    } else {
30.     SpawnTile ();
31.    }
32.  
33.   }
34. }
35. // Update is called once per frame
36. private void Update () {
37.  
38.   if (playerTransform.position.z - safeZone > (spawnZ - amnTilesOnScreen * tileLength)) {
39.  
40.    SpawnTile ();
41.    DeleteTile ();
42.   }
43. }
44.  
45. private void SpawnTile(int prefabIndex = -1){
46.  
47.   GameObject go;
48.   if (prefabIndex == -1) {
49.    go = Instantiate (tilePrefabs [RandomPrefabIndex ()]) as GameObject;
50.   } else {
51.    go = Instantiate (tilePrefabs [prefabIndex]) as GameObject;
52.   }
53.  
54.   go.transform.SetParent (transform);
55.   go.transform.position = Vector3.forward * spawnZ;
56.   spawnZ += tileLength;
57.   activeTiles.Add (go);
58. }
59.  
60. private void DeleteTile (){
61.   Destroy (activeTiles [0]);
62.   activeTiles.RemoveAt (0);
63. }
64.  
65. private int RandomPrefabIndex() {
66.  
67.   if (tilePrefabs.Length <= 1) {
68.  
69.    return 0;
70.   }
71.  
72.  
73.  
74.   int randomIndex = lastPrefabIndex;
75.   while (randomIndex == lastPrefabIndex) {
76.    randomIndex = Random.Range (0, tilePrefabs.Length);
77.   }
78.  
79.   lastPrefabIndex = randomIndex;
80.   return randomIndex;
81. }
82. }

https://imgur.com/a/bxtYpKL