Will I face a penalty for overstaying my visa if I was mistakenly given a 90-day stamp instead of the correct 30-day stamp in Thailand?

I have an odd situation. I have a US passport and the ABTC (APEC Business Travelers Card). As an American the card should only grant me the right to use the shorter lane at immigration (there are no visa benefits as the US is only a provisional member, full member country citizens get 90 days without a visa) however they recently gave me a 90 day stamp instead of the proper 30 day stamp. Question is, if they grant me a 90 day stay, will there be a penalty when I leave if they realize I was only supposed to get a 30 day stay? Thanks!