You don't calculate concentration of H
2O
2 in the titrated solution. Instead, you calculate number of moles of H
2O
2 titrated, and as you know volume of aliquot of hydrogen peroxide taken, you can calculate concentration in the ORIGINAL sample. So yes, dilution of your aliquot doesn't matter, as it doesn't change number of moles of H
2O
2.
Also, how much sulfuric acid would be enough to acidify H2O2?
Recipe from my book: put solution containing 40-70 mg H
2O
2 into 500 mL flask. Dilute to 200 mL, add 20 mL 30% H
2SO
4, titrate with 0.1n permanganate.