Group project in school

I have school project for October 31 and we need to be in groups of 4. I have to say that I'm very introvert person. I asked one of my frinds can we worked together. She said yes and that we will find 2 more people. I herd her the next day talking to 3 other girls to work with them. Again groups of 4. Her + 3 = 4. Without me. She don't know that i heard her. And i don't know what to do now. Everyone that i know already have group. I don't have that many friends and i don't know other people in that class. I'm scared. Is that my fault? Or she just don't want to work with me? Please help me... I don't know what to do about it. I have to get grade. I feel so stupid.