Well...I maybe know how to fix your issue...I had the same...
1)Check the email.
Explaination:To be honest,it's either you registered with the wrong email...or it's already registered...And if the email is correct...
1a)Make a new email.
Explaination:The old email probably is already taken by this account--
2)Change the email to the new email.
Explanation:You need to change the email into the new one you made.(Settings->Account Settings->Email)
3)Log into the new email
(And if you already are,then just skip this one.)
4)Look for the mail sent from Wattpad.
5)And confirm!
I think this might work-although,it's quite...complicated...