Buying a home involves more out-of-pocket expenses than just the down payment! In addition to your down payment, closing costs and prepaids must be paid at closing.
Your closing costs include the fees for the mortgage company and the title company to prepare and process your loan documents. There can be some miscellaneous third-party fees as well.
Your prepaids include property taxes and homeowners insurance premiums. Additionally, you will be charged a small amount of interest based on what day of the month you close.