Can I convert my 30-day SETV stamp to a 60-day at DMK airport in Thailand?

Thanks to everyone who gave their advice. I really appreciate their help. I successfully managed to get the correct stamp date.

So it might help others in the future; I originally stamped in at the Nong Khai border with a SETV obtained from Laos, but instead of getting the correct 'admitted until' date I only received 30 days. I travelled to and then asked immigration at Don Mueng International Airport (I originally arrived at the Domestic side but walked across to the international side) if they could amend the stamp date, but was informed I would have to fly back to the Nong Khai border. Today I headed to CW where I was asked to go to the k1 section. I was then informed that I was in the system with the correct dates for a SETV but the stamp in my passport was incorrect. I was given a 'Application' form to fill in (location of crossing, transport type, passport number, etc) and asked to get 4 photocopies of pages in my passport and sign each. The photocopies were of: Info page / Visa Page / Stamp (with the incorrect 'admitted until' date) / and my tm.6 info card which she had stapled to one of my passport pages). It pretty much took less than 10 mins from the moment I was first seen and was free to do - other than the photocopies (8 baht), which I got from one of the shops downstairs. Hope this helps.

@Tod ********

Apologies, I wondered if you had a idea about what my options might be? Immigration at dmk couldnt help.