You are titrating with iodate. When you add iodate to the solution, it reacts to produce I2
. Iodine either oxidizes ascorbic acid or reacts with starch showing blue color. However, reaction with starch is easily reversible, so as long as there is ascorbic acid in the solution, it will reduce iodine - thus solution is colorless. Once ascrobic acid is completely oxidized, small excess of iodine gives relatively stable color - there is no reducing agent that could remove iodine from teh solution.
Now, take a look at your reactions. If you start with one molecule of iodate - how many molecules of iodine will be produced, and how many molecules of ascorbic acid will be oxidized?
BTW, check this reaction:
C6H8O6 + I3- + H2O --> C6H6O6 + 3I- + 2H+
It is close, but not entirely correct.