If you made them all “the same way” it’s not likely you did it wrong . They do take some time to “go live”, they don’t necessarily “go live” in the same order in which you created them, and they can take varying amounts of time to “go live”.
It’s also complicated by ISPs, and browsers, caching DNS entries, as well as browsers caching pages. I’d suggest you wait a bit longer, clear all your caches, and check again - if you did them correctly they will appear eventually.
You can also go back to the Control Panel–>Manage Domains screen and check to see if they have been added. If they are “pending” you will see a small “clock” icon next to the sub-domain name (which will go away upon revisiting that page once they are “completed” on the DH end). If the sub-domains are not there at all, something went wrong and you should re-do them. If they are there, and have no “clock icon”, the you are just in the “waiting” period for DNS to make its way across the web.