Welcome to HCM.
You have missed period of 3 days and had unprotected sex 15 days back.
You took unwanted kit
pills within 72 hrs.
So need not to be much worried.
There is some side effect of this type of pill uses like early or delayed period of 7 days or more,inter menstrual spotting,light abdominal cramp
You have to wait an other 7 days for coming period and if not coming,then do a home pregnancy
test for urine HCG.
Check the result and further consult with your doctor.
Take healthy diet,maintain personal hygiene and avoid stress.