Are you sure the payment was made right away ? (not going through something like e-cheque)
If not, e-chaques take some time to be processed and scirra only provides the license once the payment is received.
If you're sure the payment has been made and you still haven't received the mail in a few hours, be sure to send a mail to [email protected]
with your paypal payment ID and the email adress linked to the paypal account.