If only I had done something!

我当时要是做点什么就好了！

youdao

Perhaps, unconsciously, I've done something to offend her.

我也许无意中做了什么得罪她的事。

《牛津词典》

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》

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

VOA: special.2011.04.24

So if in fact I wanted to make sure this was a number, I should have done something like either try and convert it to a number, which of course failed here, or put in a check to say where it is.

因此实际上如果我想确保,这是一个数字的话，我们的课程上的代码,在这里失败了，你或许应该在这里，放一个检查的东西。

麻省理工公开课 - 计算机科学及编程导论课程节选

but if you explain it to your friend that you or she should not have or should have done something,

如果你想要向你的朋友解释，或者她应该做某事的时候，

I should have 课堂 - SpeakingMax英语口语达人

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

He said Iraqi officials should have done something about this a long time ago.

NPR: Maliki Calls Blackwater's Actions a Crime

This chart made me buy cupcakes (marketers, take note) so it must have done something right.

FORBES: The Anatomy of A Recipe