I'm six years out on the same boat. I'm actually hanging out with my daughter right now! When I found out I was going to be a dad, I was ok with abortion (makes me feel gross thinking about it now) or adoption and her mom wanted to keep her.
Granted, my situation is different because her mom wanted a kid to retain a man and gain citizenship and couldn't work in my country, and now we're divorced, but let's forget that right now.
When I was where you were, I was terrified. I know your family may not seem like they want to support you right now, I felt the same way then. Now, my family loves my kid to death. Don't give up on your folks. Grandparents mostly go nuts for grandkids. It would help if you're sincere about being a dad and you let them know your plans. You need to be strong, fearless. You're doing this for your kid's future.
You need family because they can help take the burden off two young parents trying to make it in the world. They are your lifeline right now. Your girlfriend's folks might be enough, but like I said, don't give up on your family.
Don't forget about yourself and your goals. Caring for a child might be your first priority, but you'll be much more useful to that child if you're right with yourself and your family (not to mention if you finish college and get a good job!). Nothing lights a fire under you like having a child.
If it doesn't work out between you and your girlfriend, make sure you reach a comfortable situation with her and her family before you get a new girlfriend (and forgive her if she finds a new man first).
If you just can't get help from your family, drop it for a while (but not forever). Forgive them for not understanding or being angry. Talk to your girlfriend and her family. Let them know you'll need help while you get on your feet. But don't give up on your fam! They'll regret it as much as you if they don't get to see their grandkid grow up.
One last thing: being a parent is stressful at first, but as they grow, you'll see why so many people love being a parent and having kids. I find myself making all kinds of promises to myself about how I'll take care of my daughter. I try to be firm, but fair and understanding. I try to let her have a balanced role in the relationship (being a parent isn't always being in charge). Don't slip into something hateful or abusive because of early stress. Your kid's behaviour is a response to yours. Take responsibility for that and you'll be fine. Too many parents punish their kids for responding naturally to the parent's actions.
Keep us posted! If you need more advice or feel alone, please make another post!
EDIT: There are a few variations here on the "you're fucked, buddy" theme. Don't listen to them. They may sound right, but that thought doesn't do anyone any good. Have hope and learn to live with those who don't understand. People have done great things from all kinds of beginnings. Strength comes from adversity.