I used to be round-shouldered. I think this was an indication of my lack of self-confidence and because I didn't want to stand out.
この場合、次のような言い方ができますよ。
ーI used to be round-shouldered. I think this was an indication of my lack of self-confidence and also because I didn't want to stand out.
「私は以前猫背だった。これは自信のなさと目立ちたくないという表れだったと思う」
round-shouldered「猫背の」
lack of self-confidence「自信の欠如」
to stand out で「目立つ」
ご参考まで!