Raycast Snapping Problem.

Hello there im looking for solution for snaping raycast problem so

here is the code

 using UnityEngine;
 using System.Collections;
 
 [RequireComponent(typeof(BoxCollider))]
 [RequireComponent(typeof(MeshRenderer))]
 
 
 public class MouseDrag : MonoBehaviour
 {
 Transform gridSize;
 
 void Update() {
 Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
 float dist = 100;
 RaycastHit Hit;
 Vector3 targetPos;
 
 if (Physics.Raycast(ray, out Hit, dist))
 {
 if (Hit.collider.gameObject.tag == "Floor")
 {
 targetPos = Hit.point;
 targetPos.y += Hit.collider.GetComponent<Renderer>().bounds.size.y;
 transform.position = targetPos;
 }
 }
 }
 }
 

so my problem is raycast is not accurate and not working corectly

http://g.recordit.co/8Hj9LT29h5.gif

if any help thx sorry for my bad english