Intercourse has nothing to do with stopping an ongoing period.
If you are 4days overdue , you should get a urine test for pregnancy
which might have resulted from previous contacts with your husband.
The spotting which you had while performing the act can also result from minor abrasions of the genital mucosa or might be an indiaction that you would be having menses soon when the hormonal
levels are such that it leads to withdrawal bleeding.
Menses can be delayed due to several reasons apart from pregnancy.
All you can do is to rule out that you are not pregnant. Incase you turn out to be negative , you can use progesterone tablets
for withdrawal bleeding for which you need to consult a doctor personally.