The pinky is one of those fingers that you just want to snap off after you realize how annoying it can be. It's like it has a mind of its own when it's not in use. The way your hand is "set up" is the reason you can't control your pinky the way you want it to. Your tendons pull on some of your other fingers when you are setting one specific finger in motion. Watch guitarists on YouTube and you'll notice their pinkies all act differently. Some have their pinky straight out all the time, others have it curled in, or some other way.

The point is, you can't really control your pinky all the time the way you want to, so don't worry about always trying to keep it hovering over your strings. It just isn't practical to do. It's ok if it moves around a bit while your other fingers are active, but just try to focus on making the movements not as drastic. That just takes practice. Practice actually playing a lot with your pinky. That will strengthen its individual muscle and allow you to control it a little better when you need to.