Yous guys are too funny!
It would have worked out, but you installed Hardie on the risers, therefore reducing the clearance for the tile. Just not enough overhang for backer and tiles. Another reason we seldom tile wooden steps.
Actually it's normal to install the step before the riser. Had you done it the other way, it's likely the step nosing would not have "sat" correctly on the step.
Your only choice is to tile the risers, cutting the tiles to fit to the nosing. Place the un cut edge to the nosing and the cut side down leaving a gap for caulk. Also caulk to the nosing otherwise it'll crack. Hell.... may as well just caulk all the joints.