I'm sure you'll get some patronising and/or scathing replies but I'll level with you: I wanted a baby at your age. I was pregnant at 19, had my son at 20 and it was really nothing like I was expecting.
It's nothing to do with the actual parenting part, that's alright, you just cope with it like you would at any age, but it messes up your plans for everything in ways that you don't even know yet.
As a teenager you don't know yet what you want from relationships - some people stay together with their teenage sweetheart but most people grow and change and what you want changes. Your boyfriend might change and become a total wanker or just really boring, but you're stuck with him now. Better to get out and kiss some frogs before settling down with the right person IME, and you need to kiss a few frogs to find out what you don't like. Being a single parent isn't a death knell for any and all future relationships, but it makes you a target for predatory bastards and when you do meet someone nice it messes up all of the time scales. It's sad knowing that when DH and I have a child it will be the first time for him but it won't be the first time for me, we won't be able to share it quite the same. And because I'm worried about the age gap with my DS we are maybe rushing into having children earlier than we would have otherwise.
I felt really totally and truly like I'd done all of my socialising and drinking and stuff and that was over and I was done with it. I wasn't, and while you can go out and your social life isn't dead forever, it becomes so out of step with your peers, and you don't really get how the lack of freedom affects you until it's been years.
I didn't understand that I really needed to live on my own for a bit. In a house share, perhaps - I'm not made of money! - or with a partner or whatever, but just living, not being looked after by my parents, being responsible but only for myself. Trying to figure out your own issues or what the fuck you want to do with your life is hard when you have a child around who does not allow you to take a day off.
Talking of money - it's a lot easier to save and get money behind you and work up to being able to afford a house, car, etc, when you only need a small and crappy one. At your age in your position you could buy a house - if you had a baby now, you're at a triple disadvantage. Firstly you take a drop in potential income by having to work out childcare or be a stay at home mum. Secondly you haven't had time to save up any money. Thirdly, your outgoings are higher than they would have been otherwise, much higher - it's not just food and clothes and stuff but needing a big enough, safe, clean house rather than a room anywhere, needing a car depending where you live, paying for childcare if you work.
It's really hard to think long term when you're a teenager, because (sorry this will sound patronising!) you just haven't had enough life yet. You're only really starting to be independentish from about 13, possibly 12, you've had three years to live. Not even that, you still live at home, still go to school. It's not living until you get out on your own really. Don't deny yourself that. Go and do it for a couple of years at least. You might like it. And then don't agree to have anyone's babies unless you've been together for at least five years.
Why does having a baby now seem like a better option than having one later, or any other thing you can do now? Is it about not feeling like any other option is better? Or about wanting a family of your own? Because the first one is a lie, and you have far more options before having children than after, and the second won't be fixed by having a baby, but will be fixed by getting out there and learning to love and appreciate yourself. THEN you can have a happy family. It won't come easily before that point.