Help! Do I Need To Add Distilled water To My Acid In a Titration!?

I have a titration tomorrow and I want to make sure I dont mess it up on 1 little mistake! Basically, I have sodium carbonate. I know the moles and amount. I am trying to find the concentration of diluted HCl. Our teacher will give us a mustery bottle of HCl to calculate in a titration. The part im confused about is this, I will have the Na2CO3 in the burette, and 10 mL of HCl, with 3 drops of methyl orange, in the erlenmeyer flask. Do I need to add distilled water to my erlenmeyer flask or not? If I do, i want to add 15 mL. does this seem fair? But above all do I even need to add distilled water to my HCl or can I just have HCl+Methyl orange indicator and titrate my Na2CO3?? Please answer this ASAP!!! My titration is in 7 hours! Thanks! :)