Can I renegotiate a ratified contract?

[Razak Amadu]

Signed a contract to buy a house to flip as-is. No contingencies on contract. Offer got accepted. I definitely underestimated on the rehab. Brought in contractor and the rehab is almost twice what I estimated. Unless seller reduces price drastically, this deal wont work. I called the agent to ask about possible renegotiation with seller and he responded saying the contract is already ratified so that's not possible. Please help. Is there a way I can get out of this and get my EMD? or the only option is to back out and lose my EMD? Any other repurcussion for backing out other than losing EMD? PLEASE HELP!!!!!!!!!!!!!!