There are several ways of refining edges. One of them is to modify selection area and brush the excessing parts. Just click
select > modify in the menu and you will see the all of the options in Photoshop such as contract , feather , expand ect ..
Also I recommend you to use different shaped brushes for different shaped edges. For angled lines I rather a hexagonal brush than a round
one since it is sometimes easier to clean the corners with a sharp cornered brush like a hexagonal one.
If you are using round edged soft brushes than arrange the diameter so that it does not destroy the object .
Thank you very much for reading