I.N.
Been there, too. Nothing much happened. They checked me at 3 months pregnant, and they put me on a diet from then on. Like you, I gained very little during the pregnancy (well, until 7 months I actually lost some). At work, people were always amazed when I told them how far along I was. The measurements were fine all along. Unlike you, I got high blood pressure at 8 months, and I had 3 NST per week... plus one visit to the diabetes nurse, to check the sugar levels (I had to do three measurements per day until the end). The baby had to be induced at 38 weeks (they sent me to delivery straight from a NST, pre-eclampsia). She was smallish (5% weight, 16% height and 25% head), and the pediatrician that assisted the delivery wanted to confirm the age (she thought the baby looked more like 36 weeks rather than the actual 38 weeks). But all was well for the baby, except she had blocked tear ducts (that got unblocked on their own, one at 2 months, and the other at 10). She started gaining weight really fast, at 4 months she was 92% weight, 60%height and stayed pretty much around those numbers at 6 and 9 months (she's due for her 12 months this Monday). I had a diabetes test again after 6 weeks, and I failed the 2 and 3 hours ones by a little margin (which is weird, before I never got a bad 2 and 3 hours, it was always the fasting and one hour that failed for me). I put that on not moving much during those 6 weeks. I'm supposed to have another test done soon, though.
Don't stress over it, you will be fine and so will be the baby :-)