YES! It IS Ambrosia bidentata. Nice work, Scott.
This little fella is most commonly encountered along gravel roads in Missouri, but it also occurs on our glades as well as prairies in the SW part of the state. It is quite aromatic when crushed and always reminds me of summer nights, cruising gravel roads and drinking beer when I was in high school; a true Ozark right of passage.
Below is a photo of the blooming plant. Try not to sneeze.