So during optin you received paper wallet with mnemonic (24 words).
Reminder how optin in desktop wallet looked like:
During optin you even confirmed (checkbox) that you did backup of mnemonic.
I suggest search disk for this backup 
So during optin you received paper wallet with mnemonic (24 words).
Reminder how optin in desktop wallet looked like:
During optin you even confirmed (checkbox) that you did backup of mnemonic.
I suggest search disk for this backup