help with spawning objects

In my object spawning script i spawn objects after 7 seconds but when these 7 seconds were over infinite objects start spawning please help.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class RandomSpawner : MonoBehaviour
 {
     float timer = 0.0f;
 
     public int seconds;
     public int numberToSpawn;
     public int expectation;
 
     public List<GameObject> spawnPool;
     public GameObject quad;
     private void Start()
     {
         expectation = 7;
     }
     public void spawnObjects()
     {
 
         int randomItem = 0;
         GameObject toSpawn;
         MeshCollider c = quad.GetComponent<MeshCollider>();
 
         float screenX, screenY;
         Vector2 pos;
 
         for (int i = 0; i < numberToSpawn; i++)
         {
             randomItem = Random.Range(0, spawnPool.Count);
             toSpawn = spawnPool[randomItem];
 
             screenX = Random.Range(c.bounds.min.x, c.bounds.max.x);
             screenY = Random.Range(c.bounds.min.y, c.bounds.max.y);
             pos = new Vector2(screenX, screenY);
 
             Instantiate(toSpawn, pos, toSpawn.transform.rotation);
 
         }
     }
     private void Update()
     {
 
 
         timer += Time.deltaTime;
         seconds = (int)(timer % 60);
 
         if (Input.GetKeyDown(KeyCode.Space))
         {
             spawnObjects();
         }
 
         if (seconds == expectation)
         {
             expectation =+ 7;
             Invoke("spawnObjects", 0.2f);
         }
     }
 }