Hi Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concern...
One should test for pregnancy as soon as you miss your next expected period. Nordette is a 
contraceptive pills & each pill contains 
levonorgestrel 0.15 mg & 
ethinyl estradiol 0.03 mg. It could be used as emergency contraceptive as well by taking 4 pills togethar within 120 hours of sexual intercouse & 4 pills 12 hours later.
As you took 4 pills together just the next day after sex & took 4 pills 12 hours later, pregnancy possibility is very less in you despite ovulation on march 8. This is due to high levels of levonorgestrol which prevents implantation of fertilized egg.
You should now relax as pregnancy possibility is less in you. It is always better to use regular 
contraception then emergency contraception. High doses of levonorgestrel could cause 
irregular periods & many other serious side effects. Therfore your periods may also be delayed due to taking nordette in high dose as emergency contraceptive solution.To use nordette as regular contraceptive you have to take it just once daily from 1st day of your period.
Refer to your gynaecologist
Hope this information helps