@elscorcho
Good. That setting allows you to choose whatever size prefix you want, up to whatever your ISP provides. So, if you choose 64, then you only get a single /64.
I also have a /56, with a /64 assigned to my main LAN, guest WiFi, test LAN, a downstream Cisco router and I can then route another /64 to the Cisco router.
With IPv6, you get gazillions of addresses, so no need to worry about how many you use.