haha i don't need to. Lived here long enough to live here quite comfortable. I take it you are scottish by the look of your profile. The most tightest people on the planet lol.
As it was not a national holiday, only in Bangkok area you will be fine, as long as you go on monday. Dress smartly & with a smile. The most you will get is a 1 day overstay stamp. You might even get away with it under the circumstances, As you was not to know about the closure being a tourist here.