YOU SAID:

I used to sit alone doing evil all day

INTO JAPANESE

私は一日中一人で悪事を働いていた

BACK INTO ENGLISH

I've been working all day on my own.

INTO JAPANESE

一日中一人で働いている。

BACK INTO ENGLISH

I work alone all day.

INTO JAPANESE

私は一日中一人で働いています。

BACK INTO ENGLISH

I work alone all day.