Is it better to teach my son just enough to meet education standard?

I don't think you made a mistake, but if you're doing so well at home, why not home school him? My son had the same problems at school, and the choice to home school made things easier for everybody involved. The public school system basically caters to the "average" child. In the situation of a gifted or disabled child more often than not, they are lost in the shuffle. Educating your son at home will allow you to design the curriculum around him, not him and 20 other children with varying degrees of ability. Home schooling doesn't have to be done during regular school hours, you could continue to educate him within the same time frames you have already implemented.