In the past, I had eternal problems with naming stories and its chapters, as well as naming characters...
Now, I have eternal problem only with naming characters. XD But now, usually, name I made for story remains till the end, or changes no more than one-two itterations.
It's hard for me to explain how to pick proper name for your story or for chapter, so you and other poeple will love this name.
For example, considering your description of why you named story as "Punk" at first, it is actually perfect or almost perfect name in context of story, because it is short, understandable and fits with story's main plot basis.
You can choose story's name as "one-word" short descriptoiopn of the whole story, name that tells readers story's general direction and plot. Or it can be opposite - some name that adds mystery about how story would progress in the future, it can hide major plot element or twist that would appear and be understandable only at culmination of the whole story.
I personally consider choosing name for the story as important stage of writing, and finding name that would fit story perfectly is kinda fun process for me.

I like your arguments and analysis why you rejected "The Friendship of the Sharpteeth" name for your story. Ir I was you, I would rather cypher inside the name some key event of he story that would be understandable at the second half, or simply would call it something like "... bonds" - it would fit with friendship bonds between Chomper and his new friend, bonds between him and his pld friends, and bonds between leafeaters and sharpteeth kinds.
Edit:
But you can ignore me, since I still didn't release any LBT fanfic, so I am not person who can give such advices
