I doubt fuel gauge calibration would have been an issue. With 21 pax, to remain within the MTOW of 7700kg, the captain would have just filled the main (inboard) tanks, 700li each which gives just under 4 hours' endurance at a reasonable altitude/power setting, so she should of had a very good idea of her fuel situation
Casa 212 max demonstrated crosswind limitation is 20 knots, but not a limiting factor of course. What was the actual crosswind that day?