I realized as I pulled in. It was 355 for a 520 flight with my wife and kids waiting for me. My wife may have left me if I missed the flight. I emailed them to ask for rachmanus
Too late now, but may have been able to call CS and have them add the prepaid gas option to the rental before you dropped it off.
I’ve done that the other way, added full tank when picked up the car, and called CS to remove it on my way back to drop off.