A small tip -- arrive for check-in much in advance.. usually the ground staff are in a relaxed mood when they open the counters and some little jokes / good humour work well.. as said the trick is to have the backpack within the stipulated measures and it shouldn't appear that you're bogged down by its weight.. that's usually the case.. KLM outside their country of origin is usually a pain in the wrong place in this aspect.. they have a habit of sniffing out slightly heavier cabin baggage ) Lufthansa and many other European Airlines including Finnair [which the OP is flying] are usually cool..