YOU SAID:
I am sitting on my bed with my cat.
INTO JAPANESE
私は私の猫でベッドに座っています。
BACK INTO ENGLISH
I am sitting in my bed with my cat.
INTO JAPANESE
私は私の猫で私のベッドに座っています。
BACK INTO ENGLISH
I am sitting in my bed with my cat.
That didn't even make that much sense in English.