On short courses the way you round the mark can make a big difference in your finish.  If you come close to the mark, you cannot turn until your boat is halfway past the mark.  Then as you turn, you will overshoot the mark.  Also if you turn quickly, you will slow down a lot, but if you turn slowly, you will be way off course to the next mark.  Thus you need to go to leeward of the mark, turn slowly and be on the proper course to the next mark when you pass the mark.  It may appear that the boats behind you are catching up, but after they have rounded, they will have fallen back again, particularly if they took the mark too closely.