What to do...
Assuming you feel the need for an informal race, and assuming you feel the other boat is faster you need to do something. Just holding course allows the other boat to adjust and fine tune his boat and overtake you. So you need to fine tune your boat. I believe that even the best sailors (America's Cup class) are not sailing at 100% of their potential boat speed most of the time and us more casual sailors can always improve our speed. Look for the little things, no lines in the water, not too much weather helm, not pinching too high, sails set correctly up and down the luff (not just one place) are all possibilities. Next it is worth noting that speed on a sailboat does not change instantly and that it takes minutes to see the effect of small changes. Keep working the boat and doing what is right for you. What you DO NOT do is keep watching the other boat. Instead only glance at him occasionally or better yet assign a crew to do that. Your job is close at hand on your boat. If go fast is your game at hand play all your cards. And when all else fails, loose graciously and LEARN.