Autopilots usually have a way to adjust their operating parameters for the rudder input is proportional to the speed of the vessel....i.e., the slower you go, the more rudder input the AP gives the system, and conversely, the faster you go, the less rudder input you get. The speed input on your AP is probably set in a default manual mode for a faster speed that you are traveling. Look in your AP manual for speed input and you will probably find that you can change that operating parameter to accept actual speed input from your GPS or speed sensor. Try either of those and the AP should react with rudder input proportinal to the speed you are traveling.
