Flexibility
Taekwondo and the martial arts becomes a lot easier if you are flexible, not only in your legs but your lower back as well. Practise your stretching as often as you can and try and increase your flexibility.
Not many people are naturally flexible so we are all in the same boat!
Stretching tips can be found here on this website
http://www.taekwondo-training.com/taekwondo-training/taekwondo-stretching-exercises
GOOD LUCK!