What should I do about my Thai visa stamp being for 30 days instead of the paid 60 days?

Hi need some help, I paid 40 dollars at Thai embassy in hanoi for 60 day visa. Stupid me I know but I have just looked at my passport stamp when I have traveelled through emigration and they have stamped it for thirty days only. I still have the receipt and they put a ninety day visa inside passport. What are my options now, do I need to go to emigration when the month runs out or will it be OK. As they should have all this on record with the paperwork I took. Anyone had similar issues, thanks in advance. I am now on koh Tao, so the nearest offices are on koh Samui..