The fact that you're getting pain after just 25 shots indicates that there is probably more going on than just too much pressure on your ring finger. You may be dragging the string on your ring finger. This is caused by trying to consciously release the string rather than relaxing your fingers and letting the string push your fingers aside. People who have this problem often have right misses that are not caused by plucking or creeping. “Relaxing your fingers” doesn't mean telling your fingers to relax, or you would be back in the same problem of consciously trying to release the string. It means a subconscious signal from your brain to your fingers to relax. The shooter has his fingers hooked around the string at full draw, pulling to conclusion, and suddenly there is a “pop” when the arrow is gone, and the fingers are still hooked in the air. It's as if the string cut through the fingers without damaging them. Once you feel the pop, you realize it is a different feeling from the feeling of the string dragging on the fingers as you try to consciously release the shot. Until you can feel the pop, you're kind of flying blind, but eventually you'll feel it, and once you can feel the difference, your body can make it happen again and again.
In the mean time, you have a blister on your ring finger, and can't shoot very well until that heals. So this would be a good opportunity to improve your string grip. To do this, put more of a hook into your index finger, and get to full draw however you want. Keep that extra hook in your index finger after you are at full draw. Consciously relax the tension in your ring finger until it is hardly there. You will feel your ring finger move forward as you relax it. This should help it to heal, as it should be relaxed enough not to drag on the string. Once the ring finger is relaxed, keep pulling until the shot goes off, hopefully with a pop and not a drag, with tension mainly on the index finger and the middle finger. Once you learn to do this, you can ease off on the extra tension on the index finger, but keep the ring finger relaxed.