If you already reach 3 confirmation coinbase should reflect in to your balance.. if still pending you should contact the support of coinbase and tell them to refresh your wallet so that your pending transaction will be added to your balance..
This is the same as i experience before even the transaction was confirm above 3 confirmation but in my coinbase account still pending i contact the support to fix the issue and they said they will just refresh the wallet and after that the transaction was added to my balance..