Im using MSDK 4.12 on Android with Mavic 2 enterprise on the latest firmware. I upload 2 WayPoints in a WayPointMission with aircraft heading set to the direction of the flight: WaypointMissionHeadingMode.AUTO Once the 2nd waypoint is reached, I send startShootPhoto command to take a single photo but the aircraft turns to the north or west north to take the photo and when the photo is complete the gimbal turns back to the direction of the the flight.

How do I keep the gimbal heading to remain in the direction of the flight during the shot photo?

I am not sure what you mean. How do you send startshootphoto command to the drone? Do you set a waypoint action?
If you do not send the command to rotate the aircraft, the aircraft will not rotate when shooting a photo.