When i was young i smoked weed for few months and swallowed the smoke into my stomach caused gerd. how likely is it i will devolp stomach cancer?

Base line risk: There is insufficient information, however, what you described is not likely raise your risk of getting stomach over the baseline risk you had, had you not used weed. I trust you are off weed now, it messes up the brain, For good health - Have a diet rich in fresh vegetables, fruits, whole grains, low fat milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex.