Question about drug test (please answer if you know with any certainty)?

so i am going to nursing school in march and i took my drug test today. STUPIDLY i took an ativan a couple of days ago while flying. this is a benzo that will show up in my urine if they do a 10 panel drug test. i have a filled prescription for it that i just picked up at my pharmacy as proof that i obtained it legally. can the school revoke their offer of acceptance even though i have the prescription legally? will the diagnostic company contact me before they contact the school? i don't really want to explain to the dean of students that from time to time i take sedatives. anyone that has any experience, your advice would really be appreciated!!