Hi Brandon,
All should be fine if your app.yaml file has the correct credentials. Something like
DB_CONNECTION: mysql
DB_HOST: localhost
DB_DATABASE: xxxxxxxxxx
DB_USERNAME: xxxxxxx
DB_PASSWORD: xxxxxxxx
DB_SOCKET: /cloudsql/<project-id>:<region-here>:<db-instance-name>
And have this also in your app.yaml
beta_settings:
# for Cloud SQL, set this value to the Cloud SQL connection name,
cloud_sql_instances: <project-id>:<region-here>:<db-instance-name>
Give these a try and let me know if the error persist. Also ensure you have the instance up and running.
Cheers,