If only I had done something!

我当时要是做点什么就好了！

youdao

They knew they had done something terribly wrong and lied to cover it up.

他们知道已犯下了大错，并撒谎来掩盖这一错误。

《柯林斯英汉双解大词典》

Jack wasn't saying anything, but the teacher smiled at him as if he had done something very clever.

杰克什么也没说，但是老师对他笑了笑，好像他做了一件很聪明的事。

youdao

She would say this if she believed someone had done something mean, dishonest or just stupid.

VOA: special.2011.04.24

And Jenner, because he was a trained physician, because he knew something about the scientific method, did something that these more ancient healers had not done in the past, was that he wrote down what he did.

而詹纳,因为他是个受过训练的医生,懂得一些科学方法,他做了那些古老的医生们没有做的事,就是记录了自己的所作所为

耶鲁公开课 - 生物医学工程探索课程节选

How would people react when this cultural icon had done something that people perceive as immoral?

FORBES: 'Moral Decoupling:' How Consumers Justify Supporting a Tarnished Brand

We didn't know what was going on, didn't know whether he had done something.

CNN: FBI agents interviewed bombing suspect in 2011

If we had done something wrong we would have been afraid of it coming out.

BBC: Bumi: Coal miner's fate sealed after shareholder vote