Within the Admin Center, I also assigned the Microsoft Bookings application to my user. The Bookings app is available within the top-left menu in Office 365, but it keeps redirecting me to the Onboarding page mentioned above. This page tells me to "Ask you Admin," which is myself.
I'm wondering if this may be a provisioning issue and will sort itself out over time, or if there's a step I may be missing. The Org Settings and app assignment seem to be the only steps listed in order to enable access to Bookings.