No, you can't use hydrochloric acid. It won't dissolve metals. To produce mercury chloride you first have to make mercury nitrate, then convert that to mercury oxide through heating. Mercury oxide is reactive enough and can be mixed with HCl to produce mercury chloride.
And son, if you're going to do chemistry, you'll need at least a distillation setup. It's basic stuff. A minimum. Not that expensive, just order it off ebay.
Now, nitric acid has a boiling point of 83 C, water as you know has a boiling point of 100 C. So if you boil, you'll boil off the nitric acid and not the water. Just get a distillation setup. Aim for at least 63-65% concentration. What concentration are you starting with?