The file size was too large to upload to our site so I can’t see the workout. What a negative Pa:Hr indicates is that you ran faster at a lower HR during the second half than the first. If you were on an out and back course that was even slightly uphill on the way out this would cause the negative sign. The test needs to be done a flat course or a treadmill to be most accurate.
If it was flat and you got -11 then yes you chose too low of a HR or you were not well warmed up when you started the test and so warmed up by late in the test.