You can lower the days by going to this auction and it should have an "edit" button, however since this is a pretty nice bag, you should keep the days higher so people will have a chance to search up the bag and keep it on their watch list. :) Also, if you list good items like this, having longer days also makes it possible for people to earn some more points in order to bid on the auction so personally, I don't really recommend you to lower the days. Just my opinion though! :)