I don't feel ready....

Have about 3 1/2 mo left to go and I suddenly don't think I can do this. I'm in my upper mid 20s and I don't feel like I'm enough of an adult to have a baby. I'm terrified now. I'm scared I'm going to mess up. I don't know how to do this right and to raise a baby to an adult correctly. My parents were not good role models at all and I just realized I'm going to be doing this blindly. What if I mess up and it ruins my child? I still feel like I'm just a child myself who just has a lot of responsibilities. :( I'm scared.