C#: Jump function, grounded stays True

Sorry if I'm re-posting an issue or doing something wrong, this is the first time I'm asking a question here. I'm fairly new to C# and Unity, so I've followed a tutorial in order to get my character controls in order. As far as I can tell, I've done as shown in the tutorial: 2D Character Controllers

When my Player drops down and hits the Ground, the grounded variable stays True. When I press Space to jump, the jump sound is played, so the Jump if-statement is run, but the Player object does not jump, at least not as far as I can see in the game. I increased the float variable for jumpForce to 700 to see if it simply needed more force, as I've set the gravity in the game to -30 as the tutorial said... Moving from side to side works, but the jump isn't. And the grounded variable stays True, but I can still press the Space and hear the jump sound every time I press it.

I've tried looking at another post about this issue, but it hasn't helped me: can't jump in 2d? Please tell me if there is something blatantly obvious that my untrained eyes have overlooked! :)

Here is my code:

 using UnityEngine;
 using System.Collections;
 
 public class PlayerControl : MonoBehaviour
 {
 
     public float maxSpeed = 10.0f;
     public float jumpForce = 700.0f;
     private bool grounded = false;            // Whether or not the player is grounded.
     public Transform groundCheck;            // A position marking where to check if the player is grounded.
     float groundRadius = 0.2f;
     public LayerMask whatIsGround;
 
     float minValX = -6.5f;
     float maxValX = 6.5f;
 
     public AudioClip Jump1;
     
 
     void FixedUpdate (){
 
         grounded = Physics2D.OverlapCircle (groundCheck.position, groundRadius, whatIsGround);
 
         Debug.Log (grounded);
 
 
         float move = Input.GetAxis ("Horizontal");
 
         rigidbody2D.velocity = new Vector2 (move * maxSpeed, rigidbody2D.velocity.y);
         if (rigidbody2D.transform.position.x < minValX)
             rigidbody2D.transform.position = new Vector3 (minValX, transform.position.y, transform.position.z);
         if (rigidbody2D.transform.position.x > maxValX)
             rigidbody2D.transform.position = new Vector3 (maxValX, transform.position.y, transform.position.z);
     
     }
 
     void Update(){
         if(grounded && Input.GetKeyDown(KeyCode.Space)){
             Debug.Log ("Jump!");
             AudioSource.PlayClipAtPoint(Jump1, transform.position);
             grounded = false;
             rigidbody2D.AddForce(new Vector2(0.0f,jumpForce));
         }
     }
 }