Overstayed 4 days.

Hello. Im in China on 30 day S type. 3 Weeks ago I applied for business, 3 months Visa through an agent, things got delayed abit and I'm about to get my passport back tomorrow. Unfortunatly tommorow is already 34th day of my stay here, so i'll be 4 days late. I want to reenter Shenzhen same day i leave it. Would you say I should first contact local PBS, or should I go straight to the border and deal with it there? Thank you for your time.