The best advice for you is what several other agents have provided you - speak with a real estate attorney. They will look over your contract and determine the best avenue for you to proceed. Several contingencies are built into the purchase agreement: Home Inspection, Appraisal, and financing are a few that come to mind. An attorney will review your agreement and discuss with you what it will take to get you out of the purchase agreement and whether or not you will incur any penalties.
My advice would be to contact the agent that assisted you in preparing your purchase agreement and express your desires to break the purchase (if you haven't already). Communication is key in real estate transactions. Your REALTOR may be able to speak directly with the Listing REALTOR about your wishes to no longer purchase the property. Who knows, the seller may be understanding.
I still encourage you to contact an Attorney.