Your solder mask is not misaligned, your silkscreen/legend is though.
To align it you need small crosses on your artwork external to the board.
These should be aligned with crosses on your bed, if you put small bits of pcb on the bed 9usually held on with tape) to slot the PCb into before silk screening it then they need marking up so the crosses in the screen align with the markings.
Once they are aligned you might put tape on the underside of the screen so no ink comes through the crosses.
Or - if your bed allows it you can shine a light through from underneath so that you can see through the PCB and align the screen.