Delay Problem, coule be 'OnMouseEnter'?

I am having a problem where it only spawns a cube when i drag the mouse. When I single-click it doesnt even Spawn one cube! Ive placed Debugs to verify if the mouse is being picked up and it isnt on a single click :( Heres the code:

using UnityEngine; using System.Collections;

public class GridHighlight : MonoBehaviour {

 public GameObject _NONRIGIDCube;
 
 void Update(){
 }
 
 void start () {
 }
 
 // color change to red

 void OnMouseEnter() {
     
     Vector3 objectPos = transform.position;
     
         if(Input.GetKey (KeyCode.Mouse0)){   
             Debug.Log("MouseClick");
             
             Vector3 newPosition = new Vector3(objectPos.x, objectPos.y +1, objectPos.z);
     
             Debug.Log("Instantiate");
             Instantiate (_NONRIGIDCube,newPosition,Quaternion.identity);    
     }
     
     renderer.material.color = Color.red;
 }
     // change back to white
     void OnMouseExit() {
     
     renderer.material.color = Color.white;
     }

 

}