Any test can give a false positive theoretically. Were you knowingly exposed? What made you get tested? I would bet on it being correct. Sorry for the diagnosis, I feel your pain. Been 8 months since my diagnosis, but it is manageable.
Igm tests are useless. Your 1.8 igg value is clearly in the suspect low positive range. Anything lower that a 3.5 needs confirmation. The odds this is a false positive is about 50/50.