Did you mention that you had an agent?
Does the builder cooperate with agents?
In my experience, your agent would have had to take you to the site, and sign you in, in order to be recognized and paid a commission. That's how it is done here - it may vary where you are.
At this point, have your agent call the sales office, explain what happened, and see what they say. I would think in this market, they would welcome you back.......... even with your agent.