Key question -- is your home listed for sale with a Realtor? If it's in the MLS, and your agent entered the incorrect info, then he/she needs to correct it.
But if it's not for sale, and If you're just looking at public records, then you have to take that up with your county assessor's office. But watch out -- if there's an increase in your SF, then it'is going to increase your taxes! So, I would seriously consider how bad this relatively minor issue is affecting you personally before you go to great lengths to get something changed.