The replies here are correct. I was in this situation last month as I left to visit Vietnam for a week with about 5 days left on my 60 day visa. Upon return I got the usual 30 days visa exempt status.
Learn a bit about Thai culture BEFORE you come. Learn a little Thai. Please, thank-you, you are welcome and the use of Kaa or Khrup. Leave any of your cultural judgments back at home. Don't be a cheap-skate or an asshat. Be aware of taxi/tuk tuk scams. Don't rent jet skis. Drink moderately or you may do things you will regret. Don't be a monger, and no they don't love you. Don't try to save money by taking buses/trains when traveling around Thailand wasting valuable time. Local airfare is extremely affordable. Agoda is a awesome application to find great hotel and airfare deals. Slow down! Don't try to plan each outing down to the smallest detail. Relax, take the road less traveled. Cash is king. Wear a helmet if you are on a scooter. Going to rent a scooter? Be sure to have a international driver license or you just might help out the local police to finance their lunches. One of my favorite places is Erawan park. Make the effort and hike all the way to the top at Erawan falls! Don't forget to rent or bring a life preserver at the start so you can swim! The Andaman coastal area is home to places that defy description. Enjoy.. don't rush. You can come back to Thailand for a lifetime of vacations and still not experience it all.