How can we confess—in viduiy—to sins which we are quite sure we haven’t committed?
The Rambam answers this: Every aveirah listed is only a category which includes offshoots and derivatives. For example, “immorality” would include improper thoughts: inappropriate reading; improper viewing; over-familiarity with the opposite gender. Stealing includes any form of dishonesty, especially monetary. Chillul Shabbos would include anything done not in the Shabbos spirit (and many times this is even technically assur).
Also, many times we have been negligent in influencing others to the good; we are then held somewhat responsible for their sins—they are ours as well.