Although they request a credit card number for confirmation, Cal Grill won't actually charge your credit card prior to dining unless you are a no show or if there is a special package where they charge a set price (e.g. 4th of July had a set price that was charged up front). Be sure to review everything and make a copy of the reservation. If you set up an account, you can review or cancel it later by pulling up the reservation number.
It took several attempts for me to get my Cal Grill reservation on-line (1 month out). If you really want a reservation, keep checking. People cancel their reservations often and space does open up.