You didn't do anything wrong, don't second guess yourself. You can only deal with what is. Your vet has checked for a foriegn object, that's good. If the predisone is working that's even better.
If you are concerned of a growth, talk to your vet. If the situation doesn't feel right, go with your gut. A 3D X-ray and scope are how we found our answer.
I wish you best of luck.