The goal of using sulfite is to have a
MOLECULAR SO2 level that is adequate to keep bacteria, yeast, and spoilage organisms suppressed. SO2 exists in 3 forms, the SO2, sulfite and bisulphite. The Molecular SO2 form is the most active form (by far), and the percentage in each state depends on the amount of Free SO2, and the pH. What the chart is showing is how much free SO2 you need at each pH level to achieve a target of 0.8 or 0.5 ppm Molecular SO2. I'd shoot for the 0.8 ppm in most cases (the pink curve).
Now if you have added 35 ppm total SO2, you can figure about half has been bound (at least), so your free SO2 is probably no more than about 17 ppm. You can measure this with a test kit in most cases to determine what your free SO2 is so you don't have to guess.
At a pH of 3.25, you need at least 23 ppm free SO2 to have the Molecular SO2 at 0.8 ppm (the pink curve). So my guess would be that you need to add at least 12 ppm more total sulfite to get to that level. A bit more won't hurt to give you a little safety margin.
Check the links in the
thorough explanation of sulfite thread in the patron's area for your reading pleasure.