After the campaign is over, you will receive an email survey from Kickstarter in which you will select your t-shirt choices, sizes and colors and fill in your mailing address. Once that survey is returned to us, we will start the fulfillment process.
All the backers count toward the challenge (even before we announced it) so you've already done your part. You can't back twice, but please encourage your spouse, your parents, your kids to pledge even a small amount so we can reach our 20,000 backer goal.
Don't see the answer to your question? Ask the project creator directly.