Spawn Random Object script spawns too much

Hey! So i have this Spawn Script which should spwan objects in a specific area each X seconds.

 using UnityEngine;
 using System.Collections;
 
 public class SpawnGameObjects : MonoBehaviour
 {
     public float secondsBetweenSpawning = 0.1f;
     public float xMinRange = -25.0f;
     public float xMaxRange = 25.0f;
     public float yMinRange = -5.0f;
     public float yMaxRange = 0.0f;
     public float zMinRange = -25.0f;
     public float zMaxRange = 25.0f;
     public GameObject[] spawnObjects; // what prefabs to spawn
 
     private float nextSpawnTime;
 
     void Start ()
     {
         // determine when to spawn the next object
         nextSpawnTime = Time.time+secondsBetweenSpawning;
     }
 
     void Update ()
     {
         // if time to spawn a new game object
         if (Time.time  >= nextSpawnTime) {
             // Spawn the game object through function below
             MakeThingToSpawn ();
 
             // determine the next time to spawn the object
             nextSpawnTime = Time.time+secondsBetweenSpawning;
         }   
     }
 
     void MakeThingToSpawn ()
     {
         Vector3 spawnPosition;
 
         // get a random position between the specified ranges
         spawnPosition.x = Random.Range (xMinRange, xMaxRange);
         spawnPosition.y = Random.Range (yMinRange, yMaxRange);
         spawnPosition.z = Random.Range (zMinRange, zMaxRange);
         if ((spawnPosition.z < 4 && spawnPosition.z > -4) || (spawnPosition.x < 4 && spawnPosition.x > -4)) 
         {
             MakeThingToSpawn ();
         }
 
         // determine which object to spawn
         int objectToSpawn = Random.Range (0, spawnObjects.Length);
 
         // actually spawn the game object
         GameObject spawnedObject = Instantiate (spawnObjects [objectToSpawn], spawnPosition, transform.rotation) as GameObject;
 
         // make the parent the spawner so hierarchy doesn't get super messy
         spawnedObject.transform.parent = gameObject.transform;
     }
 }

but there is a weird bug which leads to the behavior that somethimes 3 objects get spawned, sometimes 5, sometimes 1... but it should only spawn 1 object. can someone spot the mistake?