Thank you, Armitage!If I remember correctly I was shown a different screen.
And I got an email confirming my pre-order.
The pre-ordered Item also appears in my Gumroad library (without download link, obviously): https://gumroad.com/library
If you don't yet have a Gumroad account, just create one with the same email address that you used to pre-order.
Once I logged into Gumroad via Facebook, I was able to do the pre-order. Guess I hadn't realized that a (logged into) account was necessary.