I'm 16, 178 cm tall and weight ~67 kg, giving me a body mass index of 21.25
The problem is that I race Go-Karts professionally, and am currently 14 kg over the minimum weight limit, which all of my 17 other competitors have managed to meet. I exercise for ~3 hours per week, eat a balanced diet and race my Kart, in addition to the exercise. My problem is that I have quite a lot of muscle for my age, but I do have the odd amount of excess skin, I like to call it, around my pectoral and thigh area.
I also smoke, but I've heard that quitting gives you an increased chance of putting on weight. What can I do to achieve my ideal weight? I have attached a photograph of myself below.