After opening, my automatic garage door creeps back down a bit

There is a sensitivity switch for both directions, open and close. If you access the garage door opener in the ceiling, you will see two adjustment screws for calibrating these. I would highly recommend following the instructions in your manual, as these are life safety adjustments! Your sensitivity for closing the door is adjusted to the positive. You just need to back it off a little. Place a 2x4 on the floor of the garage where the door comes down. and when the door hits the 2x4, it should automatically come back up. If not, you adjusted it too far. Hope this helps. and remember, check the manual for your specific adjustment procedures.