Don't feel bad. The supposed reliability of FTP numbers as indicators of cycling fitness seems to be debatable these days.

For example, I cranked out fairly good FTP results on the couple of occasions I bothered doing the test, but that's because I used to race and can still put up with a moderately high level of pain.

But non-racers who are just as fit or even fitter would likely quit their ramp tests earlier than I did and thus end up with misleadingly low numbers.