YOU SAID:

I wrote them down on a postcard and then threw it away

INTO JAPANESE

私はそれらをはがきに書いてからそれを投げ捨てた

BACK INTO ENGLISH

I threw it away after writing them on a postcard

INTO JAPANESE

私ははがきに書いた後にそれを投げ捨てた

BACK INTO ENGLISH

I threw it away after writing in a postcard

INTO JAPANESE

私ははがきに書いた後にそれを投げ捨てた

BACK INTO ENGLISH

I threw it away after writing in a postcard