Am I being undercharged for walks?

My first customer on Rover (I only started a month ago) wanted/wants me to talk her dog for an hour and I initially thought that the rate was for an hour walk not a 30 minute walk. After getting another booking, this client paid me double for an hour walk which seems more fair. So what do I do for an hour walk with the customer? I have a new booking for the month of July for 5 hours each week, should I modify the booking so the price is higher?