From the FAQ:

https://www.gog.com/support/support_view/big_fall_sale_faq_en

3) How, and when, will I receive my free game?
Once you start unlocking games, you can find the redeemable game keys by clicking on the "Unlocked" message on the progress banner. We'll also automatically email you a gift code redeemable at gog.com/redeem soon after you unlock the reward. You can claim it for yourself or pass it on to a friend. It might take a few hours for the message to be delivered, so please be patient. The codes will expire on December 15, 11:59 PM GMT.

So you should have an email with the keys.

All right.

I didn't do it. So I don't have any unlocked game.
I thought that doing so would have spoiled the games, that I already own, to give to someone else.

So I should contact support I guess...

If you have deleted the emails you have to contact support. You should have gotten the mails even if you didn't click on "unlock".

You also got a mail with the codes. Check your mail folder (and maybe the spam folder as well).

Thanks guys! Found the emails, they where spammed.

Now I can make a couple of nice gift on the forum .... :D