Zohar I 202b, Parshas Mikeitz. There is a discussion on this blatt on the subject of “gazing upon your prayers,” meaning, according to the Gemoro in Brochos (55a), a person shouldn’t investigate how well he davened after praying for a long time with good kavonno and think constantly about the requests made in davening because this brings a person to heart problems. The reason is that one will quite easily get upset if they don’t immediately see all their requests, hence the heart ache. According to that gemoro specifically this act of investigating prayer causes a person’s aveiros to be evaluated more by Hashem.
The Zohar though brings a piece of advice for those who are concerned with their prayers being answered. That is to learn more Torah. This is derived from a posuk in Mishlei (13:12) that states “Hope drawn out brings sickness of the heart, and a Tree of Life is desire fulfilled.” The Zohar explains that the Tree of Life, עץ חיים, is the Torah. So through learning Torah, is the desire expressed through תפילה realized. In relation to the aspect of sins being remembered when a person investigates his prayers and whether they were answered, the advice of the Zohar makes complete sense. In order to completely make tshuva, you have to increase in learning Torah, and hopefully generating Chiddushim as well. So as part of the general processs of becoming better people and getting closer to Hashem, we have to increase in learning Torah, which will generally assist in our requests from Hashem being answered.