sometimes your feet are going to cramp up. sorry. that is just a fact of the ballet life. sorry.
however. to keep from cramping up, you should keep tension out of your feets. point through to your toes, don’t put it all in the arch. make sure to articulate your toesies, that really helps. don’t just lock and load, move your whole foot. it really goes through the leg, from your calves, and then toes, ball of the foot, heel. jamming it will do you no favors.