There's a risk of pregnancy. Emergency contraceptives are only about 85% effective at best. The longer you wait, the less effective they are. Daily birth control is about 99% effective. Condoms are more effective, used properly, than an emergency contraceptive.
Having sex just before or during ovulation is near the peak of your fertility. Odds, without using contraception, would be about 1 chance in 5. That's as good as they get.
Remember, you can have some side effects from the pill. Sore breasts, spotting, discharge, an early or late AND heavier or lighter period are all normal. You can take a home test as early as two weeks after you had sex if you choose. You MUST use your wake up pee for the best accuracy. Testing early false negatives are common.
Hope it helps.