Many things can delay a period, like what Haz said, stress is one of them. Hormone imbalance, diet/weight change, illness, infection etc can also delay a period. I agree with Haz, wait another week and if still no period, test again using first morning urine, if negative and still no period go see you doctor.
it could b stress thats delaying ur period. I'd suggest that u wait 5 − 7 days before testing again n c how it goes from there.
Good luck!