Hello It is already 17th december, and you have to perform tomorrow I guess, so you are already too late to take any medications for preponing your period. What is your normal cycle length. One last attempt that could be made is to try to delay your period. You can take progesterone tablets ( dose depends on body weight ) and continue taking them till you want to avoid your period. After stopping these pills, you would have bleeding within 2 - 3 days normally, maximum within a week. However, the period would be heavier than usual I fear that you have already been late in taking this treatment, however wish you all the best.