First of all, on quitting smoking, congratulations are in order!
Second, the odds of having lung cancer at your age, having been a smoker for only a relatively short time and smoking only a few cigs a day are 99.9999999999999999999% in your favor! (I really want to say 100%! but nothing in life is ever really 100%).
You needn't "do" anything. Just continue not smoking and know that you have done one of the single most important things you can do to ensure yourself a chance at a long healthy life!