Q. In the Shemoneh Esrei, there is an optional prayer for forgiveness where you confess your willful  sins since childhood. I thought our slate was wiped clean every Yom Kippur and upon marriage, so why would we keep bringing them up, unless we keep doing them?
A. A. The Rambam (H. Teshuva 1: 3, based on Talmud Shevuos 13a) and other Poskim rule that Yom Kippur does not absolve and forgive sins committed, unless one does proper teshuva and repents on them completely. Therefore one may still have to continue the teshuva efforts and praying for help and forgiveness, even after Yom Kippur.
Besides, there are many madregos and steps in the scale  of the teshuva process, including teshuva meahava, or repentance based on pure and sincere love to Hashem. If achieved, the sins once committed, actually turn now into mitzvos. That is a long and continuous process that likely involves a complete lifetime of worthwhile  effort and praying.
Rabbi A. Bartfeld