Yes, there are likely to be such fanfictions. In the Naruto series, Sakura can be quite assertive and strong - willed. Her temper and skills could potentially be a source of intimidation for Naruto in the creative interpretations of fanfiction writers.
Yes, sometimes Hulk is scared of Thanos. Thanos is a very powerful and intimidating villain, and even the mighty Hulk can feel intimidated by him in certain situations.
I can't say I'm scared. They might have suspenseful moments, but that doesn't mean they scare me. It depends on the way the stories are presented and my mood at the time.
It could also be due to a misunderstanding. Perhaps there is some misinformation spread about Sasuke in the fanfiction, like false rumors that he has a hidden and malevolent plan. Naruto, being someone who values their friendship deeply, would be scared at the thought of Sasuke turning into an enemy because of these untrue stories.
One possible reason could be Kakashi's reputation as a strict and powerful teacher. Naruto might be in awe of his skills and fear making mistakes in front of him.
Well, honey. Maybe you can think of the yarn in the story as something funny, like a long, wiggly worm that just wants to play. Try to focus on the positive parts of the story instead of the scary bits.