21 Weeks Scan : Small Baby

i went for glucose test at 24 weeks n did quick scan; doc say baby weight is about 600g. she say ok normal. then recently went for growth scan at 27 weeks doc say baby weigh is about 950g but baby looks small( i don't have a big bump btw). doc say maybe because im small tats y baby small but nothing to worry about. n imagine the doc even ask me to do blood test on the spot to check if theres any problem that causes baby to be on the smaller size. upon agreeing to it, i was actually shock the amount of blood taken from. its 6 bottles of blood tube. i was quite worried to know baby is small but looking at this post with the comments really got me confuse as why mine small. i can see the big difference on weight size though. Then next week they ask to come again n do detail scan to see againif everything alright. honestly im tired.