The client requested a 1 night dogsit, when in reality it's 2 drop-ins, each one 4 hours long. We agreed on a price and now I need to change the invoice. How can I do that?

Hi, I'mam new to the ROVER community and I am wondering what is included in a night of dogsitting. Is that staying over plus a walk in the morning and a walk in the evening? Do you charge separately for walks? I am currently charging the suggested average price of $31 for a night of dogsitting, but that seems REALLY low for staying over plus two walks. Based on the average suggested dog walk price ($16/walk) those two walks alone would be $32 and adding in the stay should push it way up.
What do you all do? Do you just charge more for the dogsitting or do you charge for the walks separately?
And what about if the client requests more than 2 walks a day?