@Dana ******
, okay I deleted the off topic and comments offering just plan bad advice :(
You would not be the first person to get the wrong stamp AND seeing as it's your passport and you're responsible for the stamps IN your passport you need to go get it corrected.
Unless by some wild stretch of the imagination (which I find EXTREMELY UNLIKELY :O they gave you a month on purpose), you'll be liable for overstay after the 7 days extension denied period expires.
GO to the immigration office and confirm that the stamp was given correctly.
AND once you do, message me and let me know what the outcome was so I can open this thread back up and let you tell everyone what happened.