Hello and thanks for the query
Their are very less chance that sex one day before periods date cause pregnancy
because ovulation occurs at 14-18 day. Delayed periods might have some other reasons or you might have sex earlier. Yes you are right this is termination of pregnancy but you have a keep a check the bleeding. As you have gave medication after 6 weeks of last period their is a risk of incomplete abortion
. If bleeding continue for more than 5 days or fever
comes in between. Than go for USG abdomen and consult your doctor immediately. This may need D and C procedure.
Hope you will use protection for sex next time.