I know how it feels: You've just discovered this amazing new subcuture that describes you in every single way, and you want to completely immerse yourself in it in every single way, and you want everyone who sees you to immediately recognize you as a member of it. I've been there. I'm still there, as a matter of fact. But it takes time to look as ooky-spooky as you are inside. For a long long time (It's been almost a year for me) you will simply look at best vaugly alternative. Why? Because Goth clothes are expensive. You have to collect clothes over time, until eventually every outfit you own screams 'different'.
You can speed up this process a little by not going on that 'just discovered this amazing subculture' shopping trip. Instead save up your money slowly, treating yourself occasionally to something beautiful. Whilst saving up, charity stores are the place to be. Here you can buy anything cheap, and then mess around with it to your hearts desire. Buy a cheap, nasty fabric first to practice on. If you don't have a sewing machine, hand sewing is always an option, although of course it takes a lot longer. If your school has sewing machines, asking if you could use them at lunch or after school is also an option: Most textiles teachers will be thrilled that you have an interest in DIYing your clothes, and they might even offer you tips on DIY.
Yeah, really short post today, but I can't think of anything else to write.