fixing a variable value during coroutine

hello, i will briefly explain my situation: i have a script that:

• gets the mouse position twice;

• calculates the magnitude and the angle of the line between the two points;

• istantiates a prefab at the first position

• a coroutine that scales the prefab along the line (var lengthC)

the problem is that when i istantiate a new object before the scaling of the other object is complete, i suppose that the variable lengthC gets updated and the previous coroutine stops. is there a way to get around it? can i like call the variable inside the coroutine and while it is executing the variable will have a fixed value?

here is the code:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class SpawnaCresci : MonoBehaviour
 {
 
     [SerializeField] GameObject myCube;
     [SerializeField] float width = 1f;
     [SerializeField] float height = 1f;
     [SerializeField] Vector3 inputPosA = Vector3.zero;
     [SerializeField] Vector3 inputPosB = Vector3.zero;
     [SerializeField] Vector3 result;
     [SerializeField] Vector3 avoidBehindCamera;
     private GameObject thisCube;
     private float lengthC;
     [SerializeField] float growFactor = 0.1f;
 
     // Use this for initialization
     void Start()
     {
         avoidBehindCamera.z = 10f;
     }
 
     // Update is called once per frame
     void Update()
     {
         if (Input.GetMouseButtonDown(0))
         {
 
             inputPosA = Camera.main.ScreenToWorldPoint(Input.mousePosition + avoidBehindCamera);
         }
 
         if (Input.GetMouseButtonUp(0))
         {
             inputPosB = Camera.main.ScreenToWorldPoint(Input.mousePosition + avoidBehindCamera);
 
             SpawnAlongLine();
             
         }
 
 
     }
 
     void SpawnAlongLine()
     {
        // Vector3 posC = ((inputPosB - inputPosA) * 0.5F) + inputPosA;
         lengthC = (inputPosB - inputPosA).magnitude;
         float sineC = (inputPosB.y - inputPosA.y) / lengthC;
         float angleC = Mathf.Asin(sineC) * Mathf.Rad2Deg;
         if (inputPosB.x < inputPosA.x) { angleC = 0 - angleC; }
 
         Debug.Log("inputPosA" + inputPosA + " : inputPosB" + inputPosB + /*" : posC" + posC + */" : lengthC " + lengthC + " : sineC " + sineC + " : angleC " + angleC);
 
         thisCube = Object.Instantiate(myCube, inputPosA, Quaternion.identity);
 
         thisCube.transform.rotation = Quaternion.Euler(0, 0, angleC);
         thisCube.transform.parent = null;
 
         StartCoroutine(Scale());
 
     }
 
     IEnumerator Scale()
     {
         float timer = 0;
 
         while (lengthC > thisCube.transform.localScale.x)
               {
                 timer = Time.deltaTime;
                 thisCube.transform.localScale += new Vector3(1, 0, 0) * timer * growFactor ;
             thisCube.transform.localPosition += thisCube.transform.right * timer * growFactor * 0.5f;
             yield return null;
               }
        
     }
 }