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Differences can occur in scan results for the gestational age, but usually the accuracy will vary by +/- 5-7 days in early scans. Chances of wrong dates are possible if the difference is high between actual/scan gestational age and gestational age as per the LMP. Consider repeating the ultrasound scan and go ahead with getting HCG levels checked to confirm the gestational age. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Drink plenty of water. Take adequate rest. Maintain healthy diet.
Take care.