Not so secret baby shower

I’m due in December and my sister has been planning my baby shower for months as a surprise for me BUT it’s not a surprise now as my mums told me ALL about it. I asked that I was only told about it being planned and that I didn’t wanna know anymore details about the date or location etc to still keep it a surprise. Instead I now know the date, who’s attending, location etc thanks to my mum. My sister hasn’t a clue that I know and I feel so guilty, I’m worried that I won’t be able to act as surprised on the day. Should I tell her I know or just go with the act of surprise?