During the Recital
Nervousness is usually worst just before you start to play. Once you start, you will be so busy with the playing that the nervousness will tend to be forgotten and nervousness subsequently decreases. This knowledge can be quite reassuring, so there is nothing wrong with starting play as soon as you sit down at the piano for the recital. Some people will delay starting by adjusting the bench or some clothing item in order to have time to double check that the starting tempo, etc., are correct; this procedure is also acceptable, as it reassures the audience that you are not too nervous and is in no hurry to start. You should also mentally play the beginning at this time, with emphasis on the musical output. It is a good idea to practice starting, from several days prior to the recital. Whenever you have time, just pretend that it is recital time, and play the first few bars.
You can't assume that you won't make any mistakes because that assumption can only get you into more trouble. Be ready to react correctly with each mistake, or more importantly an impending mistake that you can avoid. It is amazing how often you can feel an impending mistake before it hits, especially if you are good at mental play. The worst thing that most students do when they make a mistake or when they anticipate one is to get scared and start playing more slowly and softly. This can lead to disaster. Although finger memory is not something you want to depend on, this is one time you can take advantage of it. Finger memory depends on habit and stimuli -- the habit of having practiced many times, and the stimuli of previous notes leading to succeeding notes. Therefore, in order to enhance finger memory, you must play slightly faster and louder, exactly the opposite of what an anxious person would do during a recital (another counter-intuitive situation!). The faster play makes better use of the playing habit, and leaves less time for moving some wrong muscle that might derail you from the habit. The firmer play increases the stimuli for the finger memory. Now playing faster and louder are scary things to do during a recital, so you should practice this at home just as you practice anything else. Learn to anticipate mistakes and to avoid them by using these avoidance methods. The important lesson here is that one trick for "playing through mistakes" is to play it slightly faster and louder. Another method is to make sure that the melodic line is not broken, even at the cost of missing some "accompaniment" notes. With practice, you will find that this is easier than it sounds; the best time to practice this is when you are sight reading. Another way to play through mistakes is to at least keep the rhythm. Of course, none of this would be needed if you have a really secure mental play, especially if you also have perfect pitch.