Thank you for all your feedback, i didnt expect so many comments.
I suspect DH intentially slipped up to be honest, i wasnt happy as I specifically said a party was not what I wanted. I had a party for my 30th and my circle of friends is much smaller now I am hitting 40. He did offer to cancel it but then I felt guilty and abit of a killjoy so here we are.
I dont know who I am pretending for, the guest I supose who all sound invested in it now. I really wish I didnt know about it.
I should clarify I wouldnt wear gym clothes for a meal out but I would be casual. This top still has its tags on and has been sat in wardrobe for about 6 weeks. I was wondering if wide legged jeans might be an option that could work?