I still see issues in your SERVO definitions and motor placements. According to your .param file, you have the setup below which does not match your diagram. For example, SERVO13_FUNCTION is set to 76 for Right Tilt but is on the left motor. This will affect yaw control. The SERVO11_FUNCTION is set to 34 which is for Motor2 but your diagram says Motor 4…and so on.
For Q_MAV_TYPE, we have always used AUTO or 0.
SERVO7_FUNCTION,41 (Motor Tilt)
SERVO12_FUNCTION,41 (Motor Tilt)
SERVO13_FUNCTION,76 (Right Tilt)
SERVO14_FUNCTION,75 (Left Tilt)
The drift turn could be a compass issue or the EKF is settling. Check the “Messages” tab in Mission Planner to see if you get an EKF YAW message. Sometimes, you need to let the plane sit a few minutes to gather satellites or move it forward on the ground to the take-off location.
My guess on your compass issue is that your have an incorrect setting (like ROTATION_NONE) for Compass 1. Have you checked the HUD to verify North, South, East, and West positions? Since your compass is near the same level as your motors, you could try a simple test to elevate it on a (4" to 6") post. If you can post an image of the compass, I can try to determine the correct orientation. The assumption here is that your Pixhawk arrow points forward.