Whatever you do, don't cut another hole in the stern deck! Your cut is fine. I think that has been clearly stated but I repeat for emphasis! Once your boat is dry that port will be very handy if you choose to upgrade your rudder to the new style- I know that's not your goal now but it gives you the option for the future. For drying the hull you should ideally have another port just aft and center of the splashguard/coaming so air circulates between the two ports. Not sure if you've done that already.