Can't you simply go back to your preferred lender?
You still have 6 months to continue 'working' on things and improving your status (loan profile) as long as it DOES continue to improve than just go ahead and use your own Lender.
A builder's preferred lender often times will be more conservative because they can't afford to be wrong if there's any chance of your loan profile taking a turn for the worst. They are basically telling the builder to go ahead and spend XX amount of money to build your home but then if it doesn't close what are they going to do?
What kind of loan have you been pre-approved for already?