Should I be doing penance for my sins?

The word "penance" is not found in the Bible, neither is the idea found there. The Bible tells us that all our righteousnesses (that is, all the best we have to offer) are no better than filthy rags (see Isaiah 64:6). It is not penance that God wants, nor mere penitence, that is, sorrow for sin, nor remorse, but repentance.