This sounds to me like a Simrad autopilot issue. The “Rudder/Counter Rudder” settings are off. Try following the Simrad manual for redoing the Sea trial which will reset rudder and counter rudder. Also, you can go into the autopilot menu at the control head and change only these two settings but this can have you chasing your tail as you guess what might work. I find redoing the Sea Trial produces the best straight line route following as the autopilot automatically figures out what works best for your vessel.