Make it easy on yourself. Don't feel any obligation to push the pace today. If you want to run fast, you can do so in the 5-K race on the weekend. Rest or an easy run. A slight change in the normal routine because of the planned race on the weekend.
Tomorrow is scheduled as a day of full rest.
Don't be afraid to make minor changes in the program at any time, as long as you don't compromise its overall direction. Use the race as a test, not only of your fitness level, but also to get a feel for the racing scene, particularly if you are not used to running road races. Most important is the chance this gives you to practice taking fluids while you run. In a 5-K, you can sometimes get away without drinking, but you won't want to do this during the half marathon, especially if the weather is warm. One way to insure you get enough fluids is to walk while you drink.