In your error message it shows you are using .ssh/my_private_key.pem with file permissions of 0777, which allow anyone to read or write to this file. This permission level is very insecure, and so SSH ignores this key. To fix the error, execute the following command, substituting the path for your private key file.
$ chmod 0400 .ssh/my_private_key.pem
Hope this will solve your error?