I right now could write an addendum talking about how I had to take the LSAT in a town two hours away, during finals week, right when I was studying for my comprehensive exams.
I would reject you if I read an addendum like this. Too whiny. You had a lot of exams.. what do you think law school will be like?
Please don't write this addendum.
What were you practicing at? Was it much higher than 164? If so, are you absolutely sure you can score higher on another real LSAT? If yes, then retake. If no... then don't! 164 is a great score and with your soft factors anything can happen. All I know is that you don't sound very confident, and based on your post alone, I would encourage you not to retake.