If it says 10.10.4, you aren't running 10.11. There is a bug in the "about" window for 10.11 which shows "OS X Yosemite" but the version is correct at 10.11.I've restarted several times and still see 10.10.4
Shake your cursor back and forth really quickly.. If it gets large, your on El Cap. But it sounds like you are still on Yosemite. Are you sure you didn't install the latest beta of Yosemite?
Yes, I can shake it and it gets LARGE. Also, my cursor. And yes, I got sucked in to the Yosemite Beta. For the life of me, I can't figure out why there would be a Yosemite Beta out when there is a new El Capitan Beta as well. What's that all about?