What you need to know
Have a plan in mind for the last windward leg
Stay between the boats behind and the finish
Sail fast and free
It is likely that the boats are spread and there is not much to gain or lose, however being the opportunist, always keep an eye out for a game changing wind shift that may gain you a few places. It doesn't happen very often but when it does you will kick yourself if you miss it.
Have a plan for the last beat. Maintain a loose cover on the boats behind and stay between them and the favourable side of the course. If the boats behind split, loose cover the ones heading toward the favourable side. Focus on positioning your boat to the centre of the course if at all possible so you can take advantage of sudden shifts either way. As you traverse up the last beat, establish which end of finishing line is closer and aim for that end.
Tension leads to pinching and loss of speed. Remember to breath and keep relaxed. Sail fast and free and you will hold your position and who knows, maybe gain a couple of places on those who loose concentration and take their eye off the boat.