Hi,
Welcome to ehealthforum,
Emergency contraception works when taken within 72 hours of unprotected event. Do not worry about its effect in preventing pregnancy (as you took in within 72 hours). Since it contains high doses of hormones in it, it can affect the period cycle and bleeding pattern to some extent. Wait for your periods to start. Do not believe in myths.
If still in doubt, discuss about this with the doctor who prescribed the emergency contraception to you.
Take care.