YOU SAID:

The first thing I did was to put the water in the bottom of my cup

INTO JAPANESE

私が最初にしたことは、カップの底に水を入れることでした

BACK INTO ENGLISH

The first thing I did was fill the bottom of the cup with water

INTO JAPANESE

私が最初にしたことは、カップの底を水で満たすことでした

BACK INTO ENGLISH

The first thing I did was fill the bottom of the cup with water