Have you selected which calendars to use in Settings in the iPhone app? Ensure events and reminders are checked in Apple Watch in the same Settings menu. Then check that under Notifications in the Apple Watch app, Fantastical has Mirror iPhone Alerts checked. Try resetting your Watch by holding down the Digital Crown and side button until the Apple logo appears. I've found a reset is sometimes needed to sync data after a Fantastical software update. I see events from both my iOS and work Exchange calendars.