So despondent, little one measuring small at nearly 33 weeks

Hi everyone, just wanted to come on and share my frustration and see if anyone else has had the same thing. I had my ultrasound at 32+3 and bubs is measuring small, and is in the 15th percentile 🥺 I don't drink, smoke, or take drugs, am a healthy weight and have picked up 6kgs this pregnancy. I try to eat healthy, take extra vitamin D, zinc, DHA, and iron alongside my normal prenatal vitamins. I don't know what I've done wrong to have such a small baby. Placenta is normal and I have low blood pressure. My partner is 1.82m and I am 1.72m tall, so we are by no means small ourselves. I feel so upset and feel like I'm failing as a mom even before she arrives. I'm quite worried as I still have 7 weeks to go and she dropped from 18th percentile to 15th from 20-32 week scan. Just wondering if others have been in the same situation and had your little one at a good weight by birth or had them catch up soon after birth. Why is my little girl so small! 😢