Wa'alaikum assalam sha! Jangan risau sangat, baby growth memang tak linear, sometimes they measure differently depending on the angle, the sonographer, semua tu normal je. One of my mum friends had the same thing, scan ke-2 showed slightly smaller measurements tapi baby came out perfectly fine at term, so don't stress yourself out lagi sebab tu boleh affect the baby. Terbaik you discuss with your doctor at the next appointment pasal the measurements and check if baby's growing steadily, tapi dari apa you describe, sounds okay je, perut kecil boleh juga just your body type or baby's position, so see your doc to put your mind at ease okay? Pregnant life stress dah cukup, jangan tambah lagi, sabar je sampai lahir nanti