I weighed exactly the same as you prior to both of my pregnancies - 52kg.

I didn't put on a gram until I was 20 weeks with both of them. With DD I put on 13kg in total, and with DS I put on 10kg. All of that weight went on from 20 weeks onwards. They were 7lbs and 8lbs born, so not scrawny babies And I put less weight with the bigger baby. The weight you put on doesn't have much bearing on the size or growth of the baby I don't think.

It's fine, you'll be packing it on before you know it lol.