Pregnancy scan

Im supposed to be 6 weeks 6 days according to the app, however i went for my ultrasound scan and shows it is only 5 weeks plus and around size of 0.2mm. But can see the heartbeat during the scan. Does that means i may actually be more than 5 weeks plus? Is this size normal for 5th to 6th week? Im worried as i have no appetite and not eating much thus worry it did not grow well#firstbaby #pregnancy #1stimemom #advicepls