Issue with Autopilot

I recently bought an EV-100 Power Autopilot last year and cannot get it to work correctly.
When I set the autopilot, the boat start moving to port and the autopilot is constantly correcting the engine. When I stop using the autopilot, the boat moves on a straight line.
I upgraded the multi function display from a C 80 to the new Es Series and continue to have the same issue.

please advise if you have any suggestions on how to correct this problem