On other banjo forums there is much discussion about anchoring and the conclusions are pretty well that, yes, it is good to anchor. Anchoring helps you orient your fingers to the strings so they (your fingers) know where they are.
Is it absolutely necessary? NO. There are a very few players who play without anchoring but it seems for must of us mortal folks, anchoring is the way to go.
Do you need to anchor with the ring and the pinky. Again, this is a no and there are lots and lots of players who only anchor with one finger.
My own experience is that is took about a year or a year and a half before I could concentrate enough on my fingers to be able to plant the ring and pinky. Before that point, I had too many other things to worry about (fingerpicks, hitting the right strings, left hand fretting, timing, etc. etc.) to be able to concentrate just on planting my fingers.
When you start out on the banjo, everything is awkward; the fingerpicks, left hand pull offs, even just holding that heavy instrument so it takes time for your body to get used to it. Keep trying to plant at least your pinky. The more you play, the more comfortable and natural it will be to just place your fingers lightly on the head (I too, used to hook my finger on the bridge. It just a a question of practice and time for you to be able to feel comfortable about placing your hand).