4.1739 g (at 20 degrees C anyway)
You need to know the temperature that you're considering, and the density of the nitric acid at that temperature. This data is available in the public doman http://www.handymath.com/cgi-bin/nitrictble2.cgi?submit=Entry
If you're considering 20 degrees celcius, then the density of 65% nitric acid at that temperature is 1.3913
Now simply use the relationship density = mass/volume, and rearrange for mass: mass = volume x density.
So the mass is 3 x 1.3913 = 4.1739 g.