1. I regret doing that.
我很后悔那样做。

2. I am ashamed of ...
我对...感到很羞愧。

3. I shouldn't have done it.
我真不该那样做。

4. If only I...
要是...就好了。

5. I should have asked you.
我要是问你就好了。

6. I went a bit too far.
我做得有点太过分了。

7. It was too careless of me to make such a decision.
我做这样的决定太草率了。