It is not uncommon for the left and right motors or servos (not sure what you have) to not match perfectly. You compensate for the difference by adjusting the servo Min, Max and maybe Trim on the Servo Output screen that you show above.
Please see Manual mode do not drive straight - ArduRover / Rover 3.5 - ArduPilot Discourse for potential help.
I have noticed that even after this procedure, I still may have a pull to one side, or see that in pivot turns only one wheel will turn rather than one turning forward and the other backward. I have been able to simply tweak the Trim a bit and fix that.
@Yuri_Rage shows a similar, but much more sophisticated process in this video.