if you are nearer to periods then the chance of ovulation is less in case of regular periods,
anyhow better to take emergency contraceptive pill
to prevent the risk,
the pill can delay the periods as you are taking in second half of cycle,
if your periods get delayed for more than 2 weeks of expected date better check for pregnancy
once as that may be because of previous acts or because of low failure rate of pill,
try to use regular contraceptive measures to prevent these in future.