On a tourist visa you must show airlines and sometimes immigration that you're leaving the country within 60 days. Bus, train, plane, etc., to anywhere outside Thailand.
Steve is correct, you're likely on a visa exempt (short term tourist w/30 day extension. Not an extension visa) So no big deal, Laksi advice sounds accurate.
You don't mention type of stamp or if you're leaving temporarily or not so cannot answer. I would do what Bangkok I.O. told you to do if a tourist just going home.