The National Registry requires that you complete a state approved EMT course. With the course you chose you had to pass the final exam to complete the course. Since that was not achieved, you don't meet the requirements to test regardless of how many hours you spent.
The school most likely has these tests as checks and balances to gauge to see if you have the minimal knowledge to successfully pass the NREMT. It would have been a dis-service to you if they passed you and allowed the NREMT to catch that you do not have the knowledge necessary to be an EMT.
If all of the students did not pass the final, then you may have a case with the school or perhaps even the state that approved the course, but I have a feeling that only a few did not pass.
Please remember that the course was not an "art appreciation course", but a course that will allow you to go out and significantly impact the lives of people. Although I have empathy for you and your struggles, I applaud the school for holding a standard and putting the public trust above all else.