There should be 2 entries in your Steam library, one for 'Divinity: Dragon Commander' and the other for 'Divinity: Dragon Commander Beta' (though I don't know why Steam is still including the beta).
If the full game isn't showing up, did you log out, exit out of the Steam client, restart it and log back in?
Games Are Missing from the LibraryYou can try exiting Steam, deleting the appcache folder (see the support article
here) and restarting.
A few people have run into this problem, so you may need to contact Steam support.