Make sure you post the event on facebook. Go to your Home page and on the left side there is a list. Select Event and it allows you to set up the event, invite others, and allow others to "Like" the event. The non profit may have a facebook page where the same can be done.
The day of the event you can use poster board and have someone stand by the entrance in an "A" frame sign and others at major intersections.
Most cable companies have a community station to list community events for FREE. Since the fundraiser is for a non profit they should have no problem posting it.
The press release does not always make its way to the community center of a TV station or Newpaper. You may want to call and make sure that it does. A personal call to backup the impersonal press release goes a lot further.
Make sure you can build on the hard work your doing so that when you try it again you build on your current results. Ask each crafter to donate an item and hold a door raffle. You can just ask for e-mail addresses and phone numbers on the tickets and use them to build up a following. A sign up sheet at the front door asking to be friends of the non profit on facebook will make it all more successful next time.
Finally, take pictures and post them on the facebook page. Show the hard work and fun that goes into the event so everyone feels connected and appreciated!