Wind! If I am right (hard to see on my smartphone) the wind is coming from the left so the plane has to point its nose a bit to the left in order to maintain the set heading. If it would point the nose straight ahead it would be blown off path to the right. Remember that the heading you are flying quite often is different from where your plane is pointing towards.
This problem that you are experiencing is primarily due to the improper use of your rudder trim. the autopilot is compensating to keep the aircraft on course, but because the rudder trim is not correctly set the aircraft will exhibit this behavior until properly trimmed.
At the top of the EADI there is a white triangle which has a top and a bottom. the bottom represents that of an inclinometer similar to that found in a Cessna commonly known as the ball found in the turn and slip indicator.
Keeping the rudder trim is very essential during flight even with the autopilot engaged and this is accomplished by adjusting the rudder trim switch in the direction which the trim needs to correct. In the case of the image that you have shown you would need several notches of right elevator trim to get centered. The "rudder trim" switch is located on the center pedestal and is activated by right-clicking for right trim and left-clicking the mouse for left trim. If you hold the respective mouse button down for more than a second it will rapidly adjust the trim. One is also able to assign the rudder trim via the FSX/P3D key bindings within the Controls section - which usually works out to be easier than adjusting your view to look down at the rudder trim
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This problem that you are experiencing is primarily due to the improper use of your rudder trim. the autopilot is compensating to keep the aircraft on course, but because the rudder trim is not correctly set the aircraft will exhibit this behavior until properly trimmed.
At the top of the EADI there is a white triangle which has a top and a bottom. the bottom represents that of an inclinometer similar to that found in a Cessna commonly known as the ball found in the turn and slip indicator.
Keeping the rudder trim is very essential during flight even with the autopilot engaged and this is accomplished by adjusting the rudder trim switch in the direction which the trim needs to correct. In the case of the image that you have shown you would need several notches of right elevator trim to get centered. The "rudder trim" switch is located on the center pedestal and is activated by right-clicking for right trim and left-clicking the mouse for left trim. If you hold the respective mouse button down for more than a second it will rapidly adjust the trim. One is also able to assign the rudder trim via the FSX/P3D key bindings within the Controls section - which usually works out to be easier than adjusting your view to look down at the rudder trim