Congratulations Amber!
I had my son when I was 19 and my mum had me when she was 16 and I love having a young mum, she's my best friend too
Agree with what everyone else has said you are still growing and every pregnancy is different so just because X happened to your friend then it does'nt mean it will happen to you too.
I don't think there is a way of distinguishing between weight gain and baby gain just eat healthily, eat enough and keep hydrated and you will be fine!
Most of all though take some time for you and try not to worry about things I know it's hard but it gets you nowhere, I spent a fair bit of my pregnancy worrying whether I would be good at this X and if Y would go wrong but all was well I now have a happy, healthy 3 year old and I would'nt change it for the world.
Everything just clicks into place once you've had a baby, somehow you just know what to do most of the time of course there are your days when you need help and advice we all do but instinct is a great thing!!!
Anyway I will stop going on now, I like to talk what can I say
Oh and just wanted to say by your post, I reckon you are going to be a wonderful mum you've already got to the protective stage