During yesterday's Ben Hashmashot shiur, our Rav read a section from Otzar Hadinim (Eisenstein) (B"N, I'll insert the excerpt later, when I have access, or perhaps someone can edit it in.) that explained why "וּלְכַפָּרַת פֶּשַׁע" is said during a leap year. He says that it is to atone for the possibility that we made have made a mistake in making this year a leap year and that would mean that we may have been eating chametz during Pesach.
I have two difficulties with this reasoning, that I hope someone can answer:
1) If this is true, why are we beginning to worry about this during Tishrei and asking for forgiveness before we even did anything wrong - if, we even did anything wrong in the first place? Shouldn't we be asking for forgiveness in Sivan after Pesach?
2) G-d gave us the commandment to decide how the calendar works which includes how to place leap years. As it is, with the fixed calendar, the placement of the leap years are correct, with the exception of the 8th year in the 19 year cycle - currently. (This is based on the current dates and is due to the "seasonal drift" problem - discussed in a few M.Y. questions.) So, why is this statement said at all? Why should we ask for any type of "forgiveness" for adding a leap year if G-d allowed us to do so, and it turns out that a year, such as this year, needs to be a leap year.