you don't need to go. Just get a copy of the online form your landlord filled in. Then take it with you for the 30 day extension. It will be in the system if landlord filled it in online.
Technically you have to leave to prevent overstay. You could overstay for four days, but, there is a risk, all be it a small one of being stopped before you exit the the country. A few days in laos or Malaysia would possibly be a nice side trip to circumnavigate this.