How good is your posture? If you are used to being slumped over a desk writing, the spine tends to curve over and the chest hollow. inwards. This can make you appear shorter - so sit up straight! Seroiusly, doing some form of exercise to correct your posture will help. There are plenty of taller people who don't like thier stature and deliberately hunch over. Some examples that will help are various martial arts, if you are keen on that sort of thing, or Yoga or Pilates. My son started Tai Chi when he was 16, and it improved his posture no end.
Ps It can go the other way - shorter people (particularly men) tend to stick the chest out and hollow the lower back. Whatever height you are, the optimum to acheive is a straight spine.