I got the samething on my bike, Trottle tube in aluminum. The think I found is the element in the grip is a spring, if you twist the grip, the sping open and you got a little bit more room. You still have to sand it down, I even pollish it with a buffer, like a mirror!!!
There is a ''bumper ring'' near the cam, even sand that one, just be careful to not be too close to have the trottle tube free of movement.
Did the same, had to cut the first one and bought a new one