Unfortunately, it's unlikely ets made a mistake. However, as TheGR mentioned, there is a handscoring option.
A few years ago, I was in same situation as you and thought the same way. How could I score so low? Did ETS make a mistake? Can I retake the test and ask the dept to postpone a decision? Unless you have good research (based on past postings from other users), it's unlikely you will be admitted to schools which require the subject gre. However, if you have good general scores then I recommend applying to schools that don't require the subject exam or apply to a masters program.
As for myself, the subject exam was a hurdle (took the exam several times but couldn't get higher than 35%). After completing a masters program in mathematics (program didn't require the subject exam), I applied to several phd programs. I was automatically denied by every program that required the subject exam, but I was admitted to a group I school in my state (didn't require the subject exam and I didn't send my results). However, I didn't receive funding , and worked as an adjunct lecturer in the nearby colleges to pay for tuition. It would've been very beneficial to have gotten funding. After a year or two, you might be able to receive financial support. Some students were able to receive financial support from the dept or through the research from their adviser.
Looking back, I think the gre subject test is a good indicator on a students knowledge of math and how they will perform in a doctoral program (in the beginning). I found the first two years in the phd program to be difficult because I had a weak foundation (which showed on the gre subject exam). From my experience, the questions I couldn't answer on the subject test (because of the topic) came back in the later courses. Also, the instructors assumed that all doctoral students know the knowledge of those topics.
In summary, if I was able to go back in time I would spend more time studying. Actually, going through all the texts and main concepts of the prerequisite areas tested on the subject exam. It will not only be beneficial for the exam, but also for yourself. All the topics will reappear later on, and this is the perfect time to solidify your foundation.