Illustrator filling color outside boundary?

Hi!

I am begginer in Illustrator.

I tried to find solutions on Google, but I could not find the answer.

I made logo draw from this tutorial https://www.youtube.com/watch?v=zMirXGBOqLQ 

But when I try to fill this logo with a gradient color, Illustrator makes filling color outside boundary. See images in attachment.

So I tried to use Pen and Curvature tools again to create new lines, so there would no be gaps, but color is still "leaking."

Questions:

1. Why does color leak?

2. Why when I create a new line on logo, it does not divide the logo in two independent parts?

What am I doing wrong?

Thank you.

Janis.