I am guessing that, as you were offered an OTA Update, your FP3+ was on a dev build. So, firstly, you are reporting a fail there! (OR an update on stable was withdrawn!)
Easy Installer installs a stable build, where an untested OTA Update should not be offered.
For the record: At this point it would have been worth to try to just go back to the prior state of the OS before the update …
You can just wait. @aibd is right, via the Easy Installer you are on the stable release channel now, the update will come a bit later there than on dev.
A/B device, first time OTA, a little nervous. If nothing goes wrong, I should be able to just click download under system updates and everything is taken care of automatically? Or is using fastboot part of what I need to do every time I OTA update?
More or less. When download completed the process pauses; press ‘Install’ to continue. When installation complete it pauses again.
Press ‘Reboot’ to continue. There will then be a pop-up saying “You are about to upgrade to eOS…etc” . It may give the wrong version number but don’t worrry, it will install the downloaded version number! Seems to be a glitch.