First, please try shutting down your device, restarting it, and then run the game again. There is a chance the item you purchased will be applied on re-start.
If it is still not showing up, double check your Google Wallet account and verify that the purchase was successfully completed.
If the purchase was successfully completed and charged, and the item was a managed item like a Coin Doubler or Starter Pack, you should be able to click on it again in game and it will give it to you without charging you.
If the purchase was successfully completed and charged, and the item was a non-managed item like a coin or gem pack, then please contact us with your order number and we will get the coins to you another way.