Sorry to hear that KNSeller,
You unfortunately are in a position alot of other homebuyers are in who have bought new in areas such as arizona or Las Vegas. WIth builders slashing prices, or offering incentives, and rate buydowns. They are making it extremely difficult to compete, if you have to sell the home.
Here is a good article on the problem. http://www.msnbc.msn.com/id/21151323/
I also would not take your Zillow estimate as a concrete value. Your best bet is talk to a realtor and ask what a real value is based on actual MLS data. You also need to make sure you check your loans and see if there are any pre-pay penalties, as well as builder regulations about selling early.