I had struggled to get rid of the offset for a day or two. Someone had the same problem before but, the solution given didn't help.
Below is a screenshot of the problem.
As you can see the first step is offset and doesn't follow the blue reference line.
The following screenshot shows how to fix this issue.
Set the value marked on A as 0 and your offset will be gone.
But since the staircase meets a horizontal slab surface, changing the cut to horizontal helps too.
Hopefully, this helps all the best.
And don't forget to always put your best foot forward!