You’re right, the dead-space should stay, that's not the problem. The thing is that there are too many in-between-steps available, if you position the knob just a little to the left or right you can even make player run in slow motion

I believe that you should maybe try it like this: if the distance from left to right is 100 points, you should make 0-10 to be used for left, 10-90 to be used for stop & 90-100 to be used for right. The reason for this in my opinion is that it's very easy to make player go right, you just go all the way to the right with your mouse, but it's very tricky to make the player stop because you need to target almost perfect middle of the circle.