No no no......ok each liter of stock solution has 105 grams, this is aprox a 10% solution, agree?
Ok so now we take 100 ml of the stock solution, now we have only 10.5 grams...(10% solution). Were are now further diluting these 10.5 grams in 900 ml..(water+C+A) to make .105 concentration of sulfite aprox. In your previous post you missed a step.

Or in other words your calculations assume that 100 ml have 105 grams not 10.5 grams. Read your post again and you will see I am correct.