Have you read the My Cloud User Manual (http://support.wdc.com/product.aspx?ID=904), specifically the section on Remote Access? Or read the my Cloud Dashboard Help? Or reviewed the following two WD websites which also explain how to setup and use Remote Access?
http://mycloud.com/learn/?id=mycloud
http://setup.wd2go.com/index.php?mod=howTo&device=mc
Officially you cannot remote map or remotely access a My Cloud drive in the manor your attempting. WD removed the capability to remotely map a My Cloud drive last year. Unofficially if one is using the older first generation v4.x My Cloud it is possible to remotely map the My Cloud but it is NOT supported by WD and requires using SSH to install the unofficial non supported module a user created.
https://community.wd.com/t/app-clouddavmod-various-versions-for-firmware-v4-12-2016/161543
