If you are 3 months clean then you probably are going through a lot of trouble for nothing. To be sure get $20.0, go to Walgreens or any other pharmacy and buy an at home kit and test yourself before your parents do. With 3 months no smoking you should pass. Be warned that with the test kit you will be using, there is an option to mail in the urine for further analysis by the co. They could note the speciman was dilluted. Also since this is an obvious concern for your parents maybe curtail your use until you get your own place and then smoke as much or as little as you want.