Yes you right, precum whiich is secreted from male organ before ejaculation may contain sperms and it may cause
pregnancy.
Next Choice One Dose can reduce your chance of pregnancy if it is taken within 72 hours (3 days) after unprotected sex, but should not be used as regular birth control pill.
Some Side effects of this drug are : heavier menstrual bleeding,
nausea, lower stomach (abdominal) pain,
tiredness, headache, and dizziness
In your case, you have taken emergency pill within 72 hours of unprotected sex, so chances of pregnancy is very less. Watch for your next period which may get delayed and if that happens rule out pregnancy and consult a doctor.
If pregnancy gets ruled out and if you are not ready for pregnancy, but intend to remain sexually active, you should consider getting started on suitable regular birth control measures to be protected (after periods). Be regular with birth control use as instructed. Avoid having unprotected sexual contact if you are not ready for pregnancy
regards
Dr Santosh