The backpack is pretty well stuffed and only 19.6kg!
I have to admit to a bit of a blonde moment. I took my backpack to Mum and Dad's room where the scales are, and it weighed in at 16.6kg. So I managed to wrangle some more stuff in there, and as I was lugging it past Mum, she innocently asked if it would make more sense to bring the scales to the backpack rather than the backpack to the scales...doh!!
My carry-on still has a couple of kilos AND there'll be plenty of room in my laptop bag. I don't know what I was so worried about! AND it's only Friday night!