Marijuana and drug test

So, this may be a silly question. But I got drunk and took one puff off of a joint at a party roughly 3 weeks ago. I have a upcoming drug test this weekend at a lab and I am terrified of failing. I took two drug store tests and they came back negative but I am still hesitant on their accuracy. Anyone familiar with how long marijuana stays in your system? I’m around 115 lb. in weight. Please no judgement. Please