Oh you poor guy! If it were me I would get the cast off right away. Casts are out of the dark ages and cause permanent nerve damage. They do not make any difference in how straight the bone heals. A study done with dogs and cats with perfectly healthy limbs- put those limbs in casts and found that there was permanent nerve damage. Sister Elizabeth Kenny did not believe in using casts either and said immobilizing limbs caused deformity. I have one son who healed his broken bone with no cast and healed perfectly and one son who had a cast and says his limb is not the same as before the accident.
Terrible. I hope you come right soon.