You're doing a really great job but there is something I want to show you.
I don't want to tell you what to do, it's just an advice.
The regular banner file looks like this:
And that's the custom banner file:
I think you have to respect those spaces between each banner because it might makes stuff like this:
The banner size must be 132x340 and must fits in those spaces to be perfectly centered.
That's pretty much it. Let me know what you think