This is kind of complicated, so I start from the beginning...
I went to Scirra's webshop (not Steam), bought Construct 2 and paid with paypal. The site said that after that, I should've been redirected to the next page for downloads. That didn't happen. Instead, after I paid with paypal, it redirected me to PayPal's account page. There was no way going back to the webshop, so I went there manually, only to see Construct 2 was still in my shopping cart. I got a receipt from Paypal, so at least funds were withdrawn; but I didn't get any redeem code (I e-mailed support about that).
I'm thinking the problem here is that I wasn't logged in (or even registered) when purchasing. I also entered wrong password for my paypal account when I bought the product first time around.