[C#] Make my 2D character jump in FixedUpdate

So, i'm trying to reproduce the Meatboy CharacterController (Meatboy, not Super Meatboy) I'm having a problem on the jump (Well, i have to precise i'm really new in C# and Unity in general)

When i press Space, my character is bumping for like 0.1s, then falling down automatically with gravity. What i'd like to do is making him jump for a while (maybe 1.5seconds), then slowing and falling down. And if possible, i would like to do eveything in FixedUpdate (i added some lines in Update, i want to replace them). I see that the problem for the 0.1sec jump is because my Jumping goes from true to false right after i pressed Space, but i don't know how to fix it.

I hope you can help me on this, because i don't really see how i can do this.

Here is my code now:

 using UnityEngine;
 using System.Collections;
 
 public class MeatboyController : MonoBehaviour {
 
     bool onWallLeft = false;
     bool onWallRight = false;
     bool onGround = false;
     bool Jumping = false;
     private float Gravity = 4;
     private float Vitesse = 10;
     private KeyCode Left = KeyCode.LeftArrow;
     private KeyCode Right = KeyCode.RightArrow;
     private KeyCode Jump = KeyCode.Space;
     private float CDJump = 2;
 
     void FixedUpdate () {
 
         Vector2 targetPos = rigidbody2D.position - Vector2.up * Gravity * Time.fixedDeltaTime;
         if (onWallLeft == false && onGround == false && onWallRight == false) {
             if (Input.GetKey (Left)) targetPos = rigidbody2D.position - (Vector2.right * Vitesse * Time.fixedDeltaTime) - (Vector2.up * Gravity * Time.fixedDeltaTime);
             if (Input.GetKey (Right)) targetPos = rigidbody2D.position + (Vector2.right * Vitesse * Time.fixedDeltaTime) - (Vector2.up * Gravity * Time.fixedDeltaTime);
         }
         if (onGround == true) {
             if (Input.GetKey (Left)) targetPos = rigidbody2D.position - (Vector2.right * Vitesse * Time.fixedDeltaTime) - (Vector2.up * Gravity * Time.fixedDeltaTime);
             if (Input.GetKey (Right)) targetPos = rigidbody2D.position + (Vector2.right * Vitesse * Time.fixedDeltaTime) - (Vector2.up * Gravity * Time.fixedDeltaTime);
         }
         if (onWallLeft == true && onGround == false && onWallRight == false) {
             if (Input.GetKey (Right)) targetPos = rigidbody2D.position + (Vector2.right * Vitesse * Time.fixedDeltaTime) - (Vector2.up * Gravity * Time.fixedDeltaTime);
         }
         if (onWallLeft == false && onGround == false && onWallRight == true) {
             if (Input.GetKey (Left)) targetPos = rigidbody2D.position - (Vector2.right * Vitesse * Time.fixedDeltaTime) - (Vector2.up * Gravity * Time.fixedDeltaTime);
         }
         if(Jumping == true){
             rigidbody2D.AddForce(transform.up*700);
             Jumping = false;
         }
         rigidbody2D.MovePosition( targetPos );
     }
 
     void Update () {
         if (Jumping == false) {
             if (Input.GetKeyDown (Jump)) {
                 Jumping = true;
             }
         }
     }
 
     void OnCollisionEnter2D(Collision2D collision)
     {
         for (int i = 0; i < collision.contacts.Length; i++) {
             if(collision.contacts[i].normal.x > 0) {
                 onWallLeft = true;
             }
             if(collision.contacts[i].normal.x < 0) {
                 onWallRight = true;
             }
             if(collision.contacts[i].normal.y != 0) onGround = true;
         }
     }
 
     void OnCollisionExit2D(Collision2D collision)
     {
         for (int i = 0; i < collision.contacts.Length; i++) {
             if(collision.contacts[i].normal.x > 0) onWallLeft = false;
             if(collision.contacts[i].normal.x < 0) onWallRight = false;
             if(collision.contacts[i].normal.y != 0) onGround = false;
         }
     }
 
     void OnGUI()
     {
         GUILayout.Label("on left wall:" + onWallLeft.ToString());
         GUILayout.Label("on right wall:" + onWallRight.ToString());
         GUILayout.Label("on ground:" + onGround.ToString());
         GUILayout.Label("is jumping:" + Jumping.ToString());
     }
 }