YANBU.
The only circumstances in which I would ever invite myself to stay somewhere is if there was already an understanding that I am welcome more or less whenever (this is the case with a couple of close friends and with dh's brother's ILs). And even then you check dates with them, ffs.
I have got very definite over the years about not giving in to this kind of 'surprise' attack to keep the peace. IIWY I would definitely be saying sorry, no can do.