Ahhh I understand, scary lah tunggu scan blik kan. Honestly masa I kena macam ni dulu, I just focus on makan well, lots of protein, iron-rich food, and proper rest je, sebab baby kena grow at their own pace. A few of my mum friends in the same situation also try to stay calm and trust the process, sebab sometimes baby just develop slower sikit tapi perfectly fine in the end. Tapi honestly, if you're worried, don't hesitate to call your doc's clinic and ask more questions, they can explain better what "small size" means for 13 weeks and what to watch for. Try not to stress too much in the meantime, easier said than done I know, but stress tak bagus for baby either!