YOU SAID:

if the watermelon doesn't frown then we are not having dinner

INTO JAPANESE

スイカが眉をひそめないなら、私たちは夕食を食べていません

BACK INTO ENGLISH

If the watermelon doesn't frown, we're not eating dinner

INTO JAPANESE

スイカが眉をひそめなければ、私たちは夕食を食べていません

BACK INTO ENGLISH

If the watermelon doesn't frown, we're not eating dinner