GED or Finish High School

I only have to have one class and my school don't take part time students and I was put in psychology (a class I don't need) a month after it started and there isn't any way I can catch up in time for graduation and if I fail it cause the guidance counselor didn't give me the username and password when it started I won't be able to graduate...I have more than enough credits to graduate but I need to take probability and statistics and that's it so these are my two choices. GED or High School even though I won't get a diploma if I fail which is likely with psychology starting a month ago.