When you booked the rental, what was the rate code and what terms were tied to it? Most rate codes have specific details ("48 hour max", "4 day min", "Saturday night keep required", etc. etc.). So if your extended terms don't meet the requirements of your original rate code, then all bets are off. You can't just rely on what they're renting 1-day cars for at that point.

And then once it's recalculated, you'll pay the $10 additional fee (plus taxes).