Hi .Does the belt click when you let it back in? You may be pulling the belt out too far when fitting it. This activates the child seat fixing and will only allow the belt to retract. This holds the child's seat firmly against the rear seat and doesn't allow it to move, much as you are getting when you use it. Try keeping the belt closer to your body when fitting it and this should help. The belt should only go into the fixing mode if pulled all the way out. HTH