It is irrelevant whether or not your university gave you credit
1) Did you take a college class in HS? Yes/No
2) did you get credit and/or a grade for it? Yes/No
3) does it appear on a college transcript? Yes/No
4) did you report on AMCAS? yes/no
Verification may be the least of your worries. While an investigation and potentially being banned from AMCAS is possible it is unlikely to happen
So here is the situation: you have submitted an application attesting to its accuracy which you wholly responsible for. You have now lied on your application. It is irrelevant as to why you didnt note the course the course, whether intentionally or oversight, it is your responsibility.
So you have two choices. First is do nothing. If AMCAS discovers it, then deal with it then. If they dont find it, If and when you get accepted you can write a "dean letter" saying an oversight on this course, particularly if it is non-science/non math course. This is trivial.
Second, call AMCAS and beg to allow an update to this. However, if you do that, it can easily lead to your entire application being withdrawn for the cycle, losing all funds and not allowed to reapply this cycle. It could, however unlikely, it could lead to being banned from AMCAS. Considering the enormous issues with AMCAS staff and responsiveness, I would go with the first choice