Probably normal, mine is similar. Did you start in the morning or arrive hot and expect it to cool down? Best to start early and many just do not have the BTU required to hold 72 in all conditions. Very common to run non stop during the heat of the day and until the sun drops before it cycles.
Do check the interior install. Remove the interior trim and take a look for poorly sealed transition to the ducting. Also verify if you have a plenum divider that it is well placed and sealed properly. This divider separates the air coming in and going out. If it is not installed well some of the air can just circulate within the unit.
