You need to tighten your compression, which is something that you need to do for regular maintenance on your scooter. There is a fine balance between your compression being tight enough to hold your HIC shim snug and loose enough to allow for your headset to spin. Remember that the weight of your bars will make your headset feel more loose when they are on, so tighten your HIC shim a little more than you think it should be. New scooters, or rebuild scooters, will often loosen up since all the parts need to break in and seat properly after some use. What you're experiencing is very normal.