Hi mate,
Your result is at the 97% -98% accuracy (test generation and type doesn't matter at this time frame), since an average would sero convert about 22nd day after the exposure and the rest sero convert within 4 to 6 week, keeping that in mind detectable amount of anti bodies would always develop after the Sero - Conversion phase
So having said that 8 week test should indicate a strong result however a conservative approach '12 weeks' result is conclusive.
For the remainder of the 3 % to 2 %, I'd say rest easy, i'ts more likely that a bus hitting you whilst you crossing the road rather than your result changing further
Regards
Mike
Since you never had a risk to begin with, of course your test is negative, and any other test you decide to do will be negative aswell
9 1/2 weeks huh? Thats very encouraging; i'd be AMAZED if it changed.
Good Luck!