You have tested negative and there should be no further purpose to question your doctor's intelligence here on a public forum.
I understand your concern that you must have read that the test needs to be stalled in for 20 minutes for an accurate result. However, that is a maximum time that might be needed for a result, if your test has already provided a indicative line, there should be no further reason to wait.
It's time for you to accept your result and move on.
What was your exposure, please?