30yr-old female. was exposed to a great amount of secondhand smoke over the past yr. am now out of that situation. now worried about getting lung cancer. have always been a healthy, non-smoker with no medical issues. should i be as worried as i am?

I would not worry now, since at your age statistically the probability of having lung cancer for second hand exposure is low. But id anytime you notice any symptoms ( cough, Shortness of breath, weight loss ... ) consult with your Primary care doctor , and may get low density CT of chest .

Whatever damage may have occurred will reverse over time. No need to worry. You can reduce your risk of cancer by adopting healthy habits: Eat a mostly vegetarian diet, avoid alcohol, tobacco and street drugs, avoid excessive exposure to sun, get HPV vaccine, exercise 30 minutes each day, drink enough water so your urine is mostly colorless.