Do not worry too much. I also experienced weight loss during my first trimesters due to excessive throw up. It prolonged up until middle of 2nd trimester then throwing up subdued. What's more important is the development of the baby. If length measurement indicated correct weeks it was supposed to, then you are good.

I remembered start gaining weight entering third semester. That is when the weight gain kicked in. I am embarrassed to say, but i gained good 'ol 20 kg overall from just mere 1-2kg at first trimester. So no worries, just hang in there.

As per baby length, yes if scan showed close to weeks, it should be fine.