What information do we need to provide in the e-mail? I presume a simple "Hey, I'd like to pick my preorder up at Gen Con" wouldn't do it, since you'd presumably need to verify the identity of the person to tell which order to cancel shipping on.
Didn't you give them your e-mail when you ordered the book? Isn't that proof of identity?Maybe you need your order number? I don't know, I'm just offering ideas. Regardless I think you need to get that e-mail in quick, they are shipping soon.
I am willing and able to evaluate and critique homebrew material. PM me a link if you want an evaluation or a critique. If this applies to you too, put this in your sig.