I would advise you to ring Flying Blue. Booking.com is not mentioned as a partner on the retro claim tool. Retro claims must always be made within 6 months.

Assuming you read everything carefully and checked that your choice of hotel(s) were not excluded (it often happens with these consolidator sites that certain hotels are excluded from earning and or burning in the site's own point schemes, so it likely extends to this one, too.

And on a different point, I would advise you to check that whichever hotel you decide cannot be found cheaper via an alternate booking source. You are likely to be paying more than the cheapest available rate going via this tool, and FB miles aren't worth paying extra for.