I put way too much gas in the rental car

I roughly calculated the distance and thought 20,000 KRW would be enough,
but when I filled it up, the gauge only went up to the level it was at when I first rented it. Hmm. Did I drive too much? Since I still have to go another 30km, I decided to add another 15,000 KRW, but that made the gauge go up one notch higher than when I started. Well, that's fine.
As I started driving, the gauge kept rising.
By the time I arrived and returned it, it was a full tank.
I think I could have just driven with the initial 20,000 KRW.
It's tricky when you aren't paying close attention to the gauge while fueling up.