You aren't doing anything wrong at all. What you are experiencing is typical hatchling behavior. They are afraid of most large objects and quick movements. Especially most moving things directed at their heads. She needs a tight fitting hide and preferably two hides that she can squeeze into to boost her sense of security. Hatchlings are notorious for being a bit nippy and hissy at times. She will grow out of that behavior as she ages and puts on weight. Relax and enjoy her. Actually it's kind of cute. Like a baby or a toddler getting a little worked up.