It depends where Trulia is receiving the data about your home. The Travis County Tax records show your Square Footage as 2650 so that is not the problem. See link.
I would recommend contacting Trulia directly to edit. They must be receiving the wrong data from their source.
Looks like Trulia is getting there info from just your 1st floor.
They give this disclaimer if you click info next to your home.
Sales history and public records
Prior sales are residential arms-length transactions. We receive regular updates from our data providers, but public record data may contain inaccuracies. Please contact your local assessor, tax, or recorder office to correct this information.
Hope this help.