YOU SAID:

I’m left handed and my left hand is in a cast :(

INTO JAPANESE

私は左手で、左手はキャストにいる:(

BACK INTO ENGLISH

I am in the left hand, the left hand is in the cast :(

INTO JAPANESE

私は左手にいる、左手はキャストにある:(

BACK INTO ENGLISH

I am in the left hand, the left hand is in the cast :(