no yum repos through subscription?

Greetings,

I've installed rhel 7.5 dev edition in a vm and have entered my subscription details but i cant do a yum update as i get this:

"This system is registered with an entitlement server, but is not receiving updates. You can use subscription-manager to assign subscriptions."

Have i missed a step? The installation instructions say the first thing to do after an install is an update (duh) but i have no access to the update repository.

my reasons for wanting to use rhel are i am in TAFE and we are doing the "Red Hat Enterprise Linux 7 Security Guide" for one of our subjects and i would like to actually use RedHat for it. But i'll accept defeat and use CentOS if i have no other options.

thanks