You step 8 is incorrect.
Here's how I would do it:
 1. DvM
 2. M-->R
 3. Sv(Q&X)
 4. R-->~S
 5. ~D            /Q
 6. M    1,5  DS   (disjunctive syllogism)
 7. R    2,6  MP   (modus ponens)
 8. ~S   4,7  MP   (modus ponens)  
 9. Q&X  3,8  DS   (disjunctive syllogism)
10. Q    9,simp    (simplification)
Edwin