This is what will happen.
If you send it back to them at your own costs they will take it. So they may do you a deal to save the bother. Ring them, not email, email guys tend not to take on board the nuance of the situation.
I did a similar thing last year, bought the Meta frameset in the sale, then the next day they massively reduced the VIP Factory Frame Kit (as above Plus reverb, saddle, fork, bars, stem, headset etc). So I bought that despite it being too late to cancel the frame. I was all ready to send back the first frame, when I opened the second one to find it had the wrong frame in… In the end they let me send back the wrong frame (a Supreme DH), and keep the meta AM. But I had to call and explain to a dude, emailing just got me a stock answer that missed the point.