I'm confused as to how you even signed a contract on a property without at least a preapproval. Most builders won't even show you the paperwork without one.
NVR wouldn't let us sign a contract until we were pre approved with their lender or an outside lender with or without earnest money.
I am surprised you only need a 600 to qualify for VA loan through WF. I called them last week and was told min score needed to be 620.
What does your realtor say about the contract. I would be sending your realtor over to talk to them like right now.