False positives are caused by the inability of the test to distinguish herpes antibody proteins in your body from other proteins.
I would say if you were farther out from the sexual contact, that it is very likely that you have a false positive here, but you are still too close to the contact for accuracy. The supplemental could be accurate or it could have been done too soon after the contact to be accurate.
I would recommend that you consider getting another igG test at 6 weeks out and see what you get. If you are still hovering around that low positive range with another supplemental negative, then wait 6 more weeks and do the blot for certainty
Terri