I posted this in another thread the other day. You'll be fine, be sure to bring your flight itinerary and fill out all of the paperwork beforehand.
Two weeks ago on a Friday I realized I left my passport in another state, and my flight overseas was at 5pm that same day. I went to the Houston passport agency around 11:15am, showed them my same day flight itinerary, and I walked out with my new passport 2 hours later. Cost me about $200. The reviews online say that people waited in line for hours, but there was a short line when I went during lunch.