Sunan-e-Muakkadah

Performing the sunnah muakkadah salaah before and after the zuhr salaah

Q: Today, my Moulana told us that if we did not read the full 12 rakaats of Zuhr Salaah, then we should go and read it. I had only read the 4 fardh and I was rushing a lot. We were writing our Jamiatul Ulama exams so I thought that if I go to read the sunnats, then I will have less time to write the paper, so I lied to my Ustaad and did not go to read the sunnats. Now I am feeling bad for deceiving and lying to my Ustaad. Will I be sinful if I leave out performing the sunnats?