It’s not enough to just look for number of errors in a usability test, you need also to consider the severity of the error. Not all usability “problems” need to be fixed.
Prioritizing your usbaility errors is important, just like defects are reported and prioritized, and tracked during unit or system testing.
It will help you know what you should fix, as well as what you have time to fix depending on your timeline. Look at frequency of the error and apply a severity indicator to each one. Then you can build a simple chart that can help you figure out what you really need to work on first to make that whole user expeience thing a well performing and positive one.