For the record, if anyone reading has done this, I truly don't get mad - it's a very common, easy mistake. So no worries, eh?
I just double-checked the WFC membership page to make sure I was on there. They have listed: Lindsay Duncan.
No, people. Lindsay Duncan is a British stage actress. She is much older and much cooler than me. (Since a lot of you just saw Alice in Wonderland, she plays Alice's mother.)
I got used to people misspelling my name at a young age. It's hard to take umbrage when it happens more often than not. I usually don't notice when editors or agents do it, but when I'm already in a bad mood, or if I already have reason to be annoyed with the individual, I take it as insult-to-injury. A few people have written back with correction / apology, and that always raises them immensely in my esteem.
But it's a constant issue for me. I introduce myself as "Lindsey-with-an-e Duncan" in any situation where the person might need to spell my name - for instance, accessing my website or sending me email. (Though once, even that didn't work, because they'd sent the email to Lyndsey.) Whenever I spell the whole name, I make sure to emphasize the E. I've caught mistakes on my name multiple times in story / galley proofs.
Sometimes I wish my parents had named me Mackenzie, which was a near thing. At least that's harder to misspell. ;-)