A came up with the idea and started the project, and I was the one who was working on it with his instructions. After it failed, out of nowhere, everybody thought I was the one who suggested doing it.
こんにちは！
ご質問ありがとうございます。
A came up with the idea and started the project, and I was the one who was working on it with his instructions. After it failed, out of nowhere, everybody thought I was the one who suggested doing it. として、
『Aさんが発案してプロジェクトをスタートし、私は彼の指示を受けてそのプロジェクトに取り組んでいました。それが失敗した後、いつの間にかみんな私が言い出したと思っていました。』と言えます。
メモ
come up with 思い付く、考え付く、考え出す
work on に取り組む
out of nowhere どこからともなく、いつの間にか
参考になれば幸いです。
日本 
