Yes, also did the same. Was on 10.11.1 PB, just turned off the Beta-Releases. Restarted just to be sure, downloaded the full installer from the App Store and now i'm on 10.11 (15A284). Everything went fine.So you came from the Public Beta 10.11.1 and just installed the official Installer and Installed 10.11 over it and had all your personal files and stuff remaining on your device? That's what I wanted to hear, great!
So this basically means: You actually can downgrade!