My boy at week 29 was around 1.2kg if I remember correctly, but every baby is different so don't stress too much if yours is a bit higher or lower. For the 3D scan, I actually did mine around 28 to 32 weeks and the images were really nice because baby still has room to move around. Just call your gynae or the imaging centre to check if they can slot you in now, most places are quite flexible with timing!