Wa'alaikumassalam sis! Alhamdulillah dapat dengar baby's heartbeat sudah, so exciting! Since period mu irregular, due date memang boleh shift sikit lagi especially dalam first trimester scans, tapi usually after 13-14 weeks dah confirm dan tak berubah banyak dah. A few of my mum friends yang irregular periods juga alami jugak this, so you're not alone! Best thing is just follow what your doctor says at the next scan, kalau doc confirm after 13-14 weeks, that's your baby's actual due date already. Just enjoy the journey and don't stress too much about the exact dates lah, baby will come when baby is ready!