YOU SAID:
I have a little sister
INTO JAPANESE
私は妹があります。
BACK INTO ENGLISH
I have a younger sister.
INTO JAPANESE
私には妹がいません。
BACK INTO ENGLISH
I do not have a sister.
INTO JAPANESE
私には妹がいません。
BACK INTO ENGLISH
I do not have a sister.
Come on, you can do better than that.