As stated, more than likely it's fine especially if it was not sitting in direct sunlight. In the summer getting the camera and film hot occasionally is almost inevitable. In any case unless there is some visible problem there is not much to be done about it. Keep using the camera and don't worry about it.
For prevention, have the camera in a bag of some sort, keep it on the floor when in the car and keep it out of direct sunlight, for example, by covering the bag with a light colored cloth. That has the added advantage of keeping it out of sight from anyone looking for a theft target. If possible open a window slightly if the car will be parked for a while with the camera inside. An insulated bag for the film and or camera might be helpful too.