Hello and thanks for the query
You have very less chances of be pregnant because usually ovulation and fertilization occur at 14-18 days of menstruation
. You have unprotected sex about 4 days back to your regular periods so no chance of fertilization unless you have done unprotected sex or used protection that have some doubt in your mind before 27.07.
To conform whether you are pregnant or not get your pregnancy
test done right now and rule it out. If it comes positive than you can try abortion
by consulting your doctor.
Hope this will help you.