Coolant refill advice

[MarkAP]

So I changed the coolant in my ‘04 S because it was green. As I am not sure what was in there (was done before I bought it). I flushed the system twice with a hose, drained it by removing the drain plug on the 3rd rad and “lifting” the hoses on the main rads with a small screwdriver (difficult to remove those hoses) and finally blow the lines out with an air hose. Refilled today with Porsche coolant using an airlift. Issue is the system only took in 5 gallons to fill when the Bentley manual says it should be just under 5.8. Heater was on on drain and filling. I also did the WP and low temp thermostat while in there.

So advice: should I drain and refill (adding another gal of P coolant)? Start over fresh with new P coolant and distilled or just call it good and drive it? FYI Chicago weather but car is garaged Nov to May.

Thanks all

Mark