Although I know the rules of PC and PP usage, I want to ask if that combination of tenses is okay. Can I use PC and PP together here?
You remember, I was writing an essay  on my computer and I have finished it .
 simply tells the person that I was doing something and it is just a fact while  emphasizes the fact that it has been finished (we don't know when, it could be finished a while ago etc). I believe I can say such sentence to somebody who saw me writing an essay and later I am telling them it is done.
Or maybe I should say it this way:
You remember, I was writing an essay on my computer and I finished it.
What about this:
I have finished the essay I have been writing.
I have finished the essay I was writing.
Are the sentences okay?
Thank you in advance.