Docker not allowing push to repo -

i'm following getting started tutorial on docker page, have image locally , have created repo via docker hub web page @ https://hub.docker.com/r/banksysan/docker-whale/.

i've got config.json so:

{     "auths": {         "https://index.docker.io/v1/": {             "auth": "secret_string",             "email": "banksysan@googlemail.com"         }     } } 

when run push though authentication error:

david@plod mingw64 ~ $ docker images repository                    tag                 image id            created             virtual size banksysan/docker-whale        latest              654156f34320        41 minutes ago      274.2 mb docker-whale                  latest              654156f34320        41 minutes ago      274.2 mb hello-world                   latest              0a6ba66e537a        3 months ago        960 b kitematic/hello-world-nginx   latest              38502dd72c08        7 months ago        7.913 mb docker/whalesay               latest              ded5e192a685        8 months ago        247 mb  david@plod mingw64 ~ $ docker push banksysan/docker-whale push refers repository [docker.io/banksysan/docker-whale] (len: 1) 654156f34320: preparing unauthorized: access requested resource not authorized 

what thing need i'm missing?