Hello, I'm 4 Weeks Pregnant Today According To My Last

Hello, I'm 4 weeks pregnant today according to my last period. Three days ago I experienced odd pulling pressure and passed tissue. I went to to emergency room where they ram tests and did a sonogram and pelvic exam. My betel hcg is 337.6, sonogram is too early to show anything and the obgyn says my cervix is closed. They said I may be having a miscarriage but I'm still optimistic. Please, I need advice. Help?!