An Unfortunate Misunderstanding

Need advice folks.

So class dinner last night with a big table of mums all chatting. I ended up sitting a few people away from a friend of mine who is in my bookclub which I'm organising next week. It was very loud and lots of noise, so our conversation went something like the following......

Me: "So bookclub dinner finally next week!"
Her: "Oh, I'm not sure if I can make it coz 5 of us are heading away for a girls weekend the next day and I'll need to pack"

Now these girls are very tight, close friends and they do their weekends semi regularly, they are all also in the bookclub, so I started thinking about how 5 of them were likely to cancel out of bookclub and all of the ramifications of reorganising. ..

Me: (Grimace) Oh stink, well it will be a nice weekend.
Her: Well, see I don't mind about who comes, you know I have an open door policy with most things, but a couple of them would rather just have it as just the 5 of us and no others, so sorry...

Conversation moves on...

Aghast I realise that she thought I was disappointed that I wasn't going and worse, that I was trying to invite myself along.

NOOOOOOO!!!!!!!!

By the time I had this realisation it was too late to back track and try and salvage my pride.
What should I do?
A: Walk away and leave it, swallowing my mortification and pride?
B: E-mail her with a clumsy, belated explanation (coz I'd need time to structure my sentences in a witty, natural way)
C: Get advice from my friends out there who may read my blog occasionally (ie pass the buck)
D: Hope that Cindy is reading this post and can do my dirty work for me over a wine with the girls on your girls weekend? (Cindy, help?)

Sheesh...
Did you all have a laugh at my expense again.