Worried sick health nut

Hey all. I know I'll probably get a lot of crap for this, but I'm a bit of a health nut and genuinely concerned. Within the past 8 months, I've smoked one pack of cigarettes. I'm 20 years old and scared for my life. I literally can't stop hyperventilating because I have really bad anxiety and I'm afraid of getting cancer or a disease. I just smoked what I'm deeming my last cigarette. I brushed my teeth, oil pulled with coconut oil for 30 minutes, then brushed my teeth again. I also don't really inhale when I smoke. I'm so scared though. Is there anything I can do (on top of quitting) that will promote lung and mouth health and prevent cancer?