Made a couple noticeable errors in my tkd form at test & answered some q's poorly. at which point would I fail?

When grading, your performance in training is taken into consideration also. Mistakes are made and it is probably just nerves. I had my grading for blue belt on Thursday and on the last 3 step I ended in the wrong stance. I also could not measure up because of a hip injury but I still broke my boards. Again, if you perform well in training this will save you in a bad grading unless you do absolutely everything wrong so don't worry about.