Welcome to Android Central! For future reference, most people do the factory reset after the update.
It's possible that your device got sent to the end of the queue after resetting, although it's pretty late now. Some people might recommend the trick of clearing the Google Services Framework, but I would be cautious about this, since Google engineers themselves have warned against doing it.
On older devices, I recall the trick of manually setting the date ahead by about a year or so, then checking for a system update again. Not sure if that really works any more, but it's worth a try. Ultimately, you could always sideload the update.
How to manually update your Nexus | Android Central