The charges you are seeing are just pre-authorizations for each reservation you create. You are not charged for the service until you select a driver to complete the reservation. If you do not select a driver for the reservation, the charges will be released from your card within a few days. If your account has any reservation credits, the credits will be used; you will still see a pre-authorization but your card will not be charged.
Please note, if you have multiple credit cards on file and the first card declines, the next card on file will be charged.