I made a similar mistake. I saw it, but saw no clear way to post different addresses for shipping and billing. I asked if there was a way on their facebook page, figuring that if I got an answer explaining how, I would pay (was planning on a $10 payment actually), and than if I didn't get an answer, I would just opt for $0 payment and put in my shipping address.

I then went about my business, completely forgot about the question I asked on facebook (because they never answered), and never ended up submitting the form.

Oh well.