First, if you regret something something that you did not do in the past and you use the verb could, you do not use the past perfect tense but you use the form COULD HAVE DONE something.
Second, we use the from I WISH somebody WOULD do something, if we are angry and we would like someone to change their behaviour right now and keep it changed in the future too.
Third, in wish clauses we can use WERE instead of WAS and it is still correct.
At BBClearningEnglish.com they publish great materials for learning English. However, most often than not they publish their material as an mp3 file instead of video. That is why I have turned their wonderful Grammar Challenge on regrets into the following video.