and i honestly don't know if there's scientific evidence to
back the first up.

first, don't don't let the cup grab the first couple seconds of
your urine stream. apparently most of the toxins build up
in the beginning. this could be total nonsense, though.

second, to keep your mind at ease, try buying an at-home
test to do at home. i did this for amphetamines when I took
a few adderall studying for finals before an internship drug
test.