A great quote that I am fond of (which encourages self-censorship of computer usage) is “You can delete your cookies, but you can never delete your memories”.
Sorry.
On a more upbeat note, there is a Chassidishe vort relating to the parsha of Viduy Maaser that concludes one should always put out of his mind the mitzvos that he has done, and Hashem is trustworthy to remember them for you. But one should always remember his aveiros (and hope that Hashem will ignore them as a result).
I have also learned that on Yom Kippur you should do tshuva even for aveiros that were already forgiven on a prior Yom Kippur. So don’t try to pretend that the aveira never happened. But no, that does not mean that your tshuva is not accepted.