Urinary pregnancy test may not turn out to be positive . From the description of your dates it appears that the chances of becoming pregnant are quite low. Contraception so late will not help.But one should not take a chance. Wait for a week and get blood levels of Hcg done. Get the report analysed by a gynaecologist.

Hello Rency ,
Welcome to HealthcareMagic forum.
Please do not panic . Intercourse during the menses or just one day prior is less likely to result in pregnancy though in rare cases it is not impossible. Pregnancy kits detect the level of hcg an hormone produced in pregnancy and excreted in urine which may or may not be detected if the period of gestation is less than a week. If you have had intercourse prior to 25th also then you should go for urine pregnancy test. If you have had sex only once and within last 72 hours then it's advisable to take an emergency contraceptive .
As of now if it's past 72 hrs then the next best thing to do is wait for a week from your due date for your periods which may be delayed due to stress or any other reason . If still you don't get your menses then please confirm the pregnancy by urine or blood pregnancy test and consult a gynecologist for termination or continuation as per your wish .
Remember to always use barrier contraception in future as it will protect you from unwanted pregnancy as well as sexually transmitted infections.
As of now don't stress , as stress can cause hormonal disturbances and postpone periods even in non pregnant condition .
Hope this information is helpful to you.
Wishing you good health
Regards