How about the props? Are you sure you got the correct ones (CW or CCW) in the correct positions?
If you draw some lines do you get this?
![]()
The green being the FCB. It can be shifted a bit up or down (blue line) but it needs to centered side to side.
How about a top view of your quad.
If you are only using stabilization and no auto-level (The I value will start to get a tiny bit off over time like this) you can put the FCB anywhere on the frame as the angle is the same, I tried mounting it on an arm to test this and was surprised to see it worked great in 'rate' mode (just stabilization no auto-level). Most FCBs also support offset if you ever had a reason to mount it rotated a bit (like on some + frames that you might want to be an X).