Should I extend my tourist visa for another 7 days or pay the overstay fee?

You might not realise/believe that if you get stopped by the police as an overstayer, prior to getting to immigration, you'll be off to the IDC then eventually deported at great expense and banned.

NEVER OVERSTAY !!!

@Robert ******

has given you good advice. Do border run NOW.

First of all there is no 7 day Extension of Stay. You can apply at the Immigration Office for a new Extension of Stay and than it the decision of the Immigration Officer to deny your application and tell you to make a border run for a new 30 day Visa Exempt entry or accept the application and stamp your passport application is not approved and give you 7 days to leave the country. As you mention you booked a flight 9 days later than your Admitted to Stay, the best option you have is to make a border run for a new Visa Exempt Entry.