I am afraid that you can only be completely confident in the reliability of that test under two different circumstances:
1.) The urine should have been in your bladder for at least 2 hours.
2.) The urine needs to be 'first catch' or 'first stream'.
If this is not the case, one cannot fully trust the result, even though it is highly reassuring as it can often be detected if the above conditions have not happened. However as your result was negative, it is difficult to have complete faith in that result.