Ay nako, totally get the overthinking, mama, I was exactly like you with my first! A few of us mums from my circle din nag-worry about the same thing, and honestly it's something na kailangan talaga i-discuss with your OB next week kasi biometry measurements can vary from baby to baby, and sometimes it just means your little one ay mas maliit-type lang pero healthy pa rin. Pero since may concern ka about the growth at proportions, definitely bring this up sa doctor pagdating mo para ma-monitor properly, don't wait pa, and if you're really anxious, pwede mo ring i-call ang clinic ngayon para mag-update or ask kung kailangan ng earlier checkup. Sending you hugs, first-time jitters are real!