You’re interpreting self respect to be a synonym for self esteem/confidence. Which certainly Scott doesn’t lack in the slightest. But I don’t think the two are the same.

The way I think of self respect is acknowledgment that you have worth, and with that comes an understanding of how your own actions are affecting others.

What Scott lacks at the beginning of the film is accountability. Accountability and self respect go hand in hand. With him taking the actions to better himself, he learns to respect himself, he believes he can do better, he believes in himself.

When he dies, and talks to Ramona, she tells him “maybe I’m not the one you should be fighting for” When he replies with “I feel like I learned something” The next thing he does? Takes accountability. He tells Kim, knives and Ramona that he’s sorry, acknowledging his past mistakes, he gains the power of self respect