Hi. I Smoked About Four Hits Off A Blunt December

Hi. I smoked about four hits off a blunt December 13th. I took two "first check" drug tests yesterday and it read negative but with very faint lines. I am worried they were wrong. I have been drinking a lot of water today and will in the morning before my test. Do you think I can pass? I weigh 120, 5'3". It's been 21 days.