If I'm not mistaken, the code should be visible via your account, not strictly through e-mail. At least, this is how the pre-order code seemed to work when I pre-ordered Heavensward CE.

I don't believe cancelling your order will be an issue, as I've already heard accounts of people who used paypal to pre-order over a month ago, paypal canceling their "hold", and being forced to order again, and ending up with extra pre-order codes they couldn't use (because their account still flags them with early access).

Worst case scenario, the flag gets removed and you'd simply use your new pre-order code.