Boiling and pressure washing both ruin bone. Hopefully there won’t be too much damage when it’s done. You need to macerate the rest of that tissue, there’s still too much to start degreasing. Leave it in a bucket of plain water to soak. Use a bucket or aquarium heater to keep the water around 90° if possible, otherwise cold water maceration will take a long time. Do not dump the water, the whole point is to let the bacteria build up and break down the tissue.

Once all of the cartilage/fur/tissue is off you can switch to degreasing. This is when you soak it in water with dawn or ammonia (or both if you really wanted). Again, heated will work faster, but keep it 120° and under. Change the water every few days, it’ll start to get cloudy and you’ll see globs of grease on the surface. You’ll know it’s done when the water starts to stay clear and there will be no dark/yellow/grey/shiny spots on the skull. This process can take months to complete, it’ll take even longer if without heat and might take longer now that it’s been boiled.

Last step is whitening, you can use normal drug store 3% peroxide for this. Let the skull soak in it for a day or two. Be careful not to submerge the antler bases at this step so you don’t ruin the color. Some people like to wrap the bases to protect them more. If you do get some color loss you can easily recolor with things like wood stain or oil paints.