Well that’s interesting that you chose to set the ATC_HOVR_ROL_TRM to zero. Hopefully you understand why the code has that parameter. Now you have set it to zero, the aircraft in stabilize mode will now want to drift quickly to the left when you center your stick. Unless your rotor spins in the opposite direction. What direction does your rotor spin when you look at it from above. Typically the RC aircraft rotors spin clockwise and is why a positive roll angle is used for the ATC_HOVR_ROL_TRM.
The rotor is CW. We set
ATC_HOVR_ROL_TRM to zero because the vehicle always drift to the right in stabilize mode when center my stick. And it also helps to prevent leaning right when take off.