The reason the fin side goes to the front of the car is because the board rocker is almost flat on the back of the board and it won't push the board down or even push to board up off the racks.
You should never leave a fin on because you can hit something and bust your box or maybe even the board. Every time I see a guy with the board like you like to do it I just laugh because we know is a beginner. New comers are always welcome. Enjoy windsurfing no matter how you put your board in the racks but not fin back and even better with no fin.