2D raycast only returns true.

Hi everyone I'm new to unity scripting so sorry in advance if this is a noob problem. Anyway I have a 2dgame where I'm using ray-casts to see if a character is grounded if it is it should be able to jump once using space-bar or up arrow then cannot jump again until it is grounded here is my code.

 using UnityEngine;
 using System.Collections;
 [System.Serializable]
 public class twoDPlatformer : MonoBehaviour {
     
     public float jumpSpeed;
     public BoxCollider2D trigger;
     //public bool isGrounded;
     public Rigidbody2D target;
     public float Speed;
     public bool doubleJump;
     private PolygonCollider2D colide;
     private float distToGround;
     private int layermask;
 
     // Use this for initialization
     void Start()
     {
         trigger = GetComponent<BoxCollider2D>();
         target = GetComponent<Rigidbody2D>();
         //doubleJump = true;
         colide = GetComponent<PolygonCollider2D>();
         distToGround = colide.bounds.extents.y + 0.1f;
         layermask = 255 >> 1;
     }
         
     // Update is called once per frame
     void FixedUpdate () {
 
     }

     bool isGrounded()
     {
         return Physics2D.Raycast(transform.position, -Vector2.up, distToGround);
     }

     void Update()
     {
         /*if (Input.GetButton ("Right")) {
             target.velocity = new Vector3(Speed,target.velocity.y,0);
         }
 
         if (Input.GetButton ("Left")) {
             target.velocity = new Vector3(-Speed,target.velocity.y,0);
         }
         
         if (Input.GetButton ("Right") && Input.GetButtonDown ("Jump") && isGrounded) {
             target.velocity = new Vector3(Speed,jumpSpeed,0);
         }
         if (Input.GetButton ("Left") && Input.GetButtonDown ("Jump") && isGrounded) {
             target.velocity = new Vector3(-Speed,jumpSpeed,0);
         }
         if (Input.GetButtonDown ("Jump") && !isGrounded && doubleJump) {
             doubleJump = false;
             target.velocity = new Vector2(target.velocity.x,0);
             target.velocity = new Vector3(target.velocity.x,jumpSpeed,target.velocity.y);
             */
 
         //Ray2D myRay = new Ray2D(transform.position, -Vector2.up);
         //Debug.DrawRay(transform.position, -Vector2.up, Color.black);
         //Debug.Log(Physics2D.Raycast(transform.position, -Vector2.up));
         
         Debug.DrawRay(transform.position, -Vector2.up, Color.black);
   
         if (Input.GetButtonDown("Jump") && isGrounded())
         {
             target.velocity = new Vector2(target.velocity.x, jumpSpeed);
         }

         if(Input.GetButtonDown("Jump") && !isGrounded() && doubleJump)
         {
             target.velocity = new Vector2(target.velocity.x, jumpSpeed);
         }
     }
 }
 

My problem is the ray-cast only returns true and idk why and when i get it not to return true (which is difficult) it doesn't work properly.

Any help would me much appreciated.

P.S Sorry about the messy code.