Code help

Hi guys, im trying to put together a simple mini game
12 Coins, match 3 you win.

So far i watched a YouTube clip showing how to make a Coin Flip but if you keep pressing it it keeps flipping.
What i want is a Random Selection and how to only Flip Once.

Here is the code i have

Code (CSharp):

1. public class CoinScript : MonoBehaviour
2. {
3.     SpriteRenderer spriteRenderer;
4.     public Sprite[] sides;
5.     int flipCount = 1;
6.  
7.     private void OnMouseDown()
8.     {
9.         StartCoroutine(WaitPlease(0.0001f, 1.0f));
10.     }
11.  
12.     IEnumerator WaitPlease(float duration, float size)
13.     {
14.         while(size > 0.1)
15.         {
16.             size = size - 0.07f;
17.             transform.localScale = new Vector3(1, size, 1);
18.             yield return new WaitForSeconds(duration);
19.         }
20.         spriteRenderer.sprite = sides[flipCount % 2];
21.         while (size < 0.99)
22.         {
23.             size = size + 0.07f;
24.             transform.localScale = new Vector3(1, size, size);
25.             yield return new WaitForSeconds(duration);
26.         }
27.  
28.         flipCount++;
29.     }
30.  
31.     private void Awake()
32.     {
33.         spriteRenderer = GetComponent<SpriteRenderer>();
34.     }
35. }

Here is a Sample Picture of what im doing



Thanks in Advance.