Shape builder tool, what am I doing wrong

[Jakub4]

Hi, Im using shape building tool to erase a line: 

But everytime I do, it also erase colour from the places I dont want to:

Can anyone please help me understand what am I doing wrong and how can I make it right? Im new to it.

Thank You.

[rcraighead · Accepted solution]

Erase the "Shape" instead:

[Jakub4]

Thank You:)