with bad teachers there are generally 2 ways to deal: teach yourself or get a tutor. if the teacher is bad at marking/biased then consult the principal as there is nothing you can do on a personal level.
ah the pressures of being dux... no one will care as long as you have performed your best :)
personally i am crapping myself because playing with some uai calculators, a few lower marks equate to a significantly lower uai :(