Illustrator Assets with borders

Hello to all,
I have created some Icons for web, that consist of different layers,
for the background I wanted to add some images by "Draw inside tool" then export them with assets,
but since some of the images had to be scaled, the assets had also a border around them, and was not limmited to the box it self.

Can anyone give me a solution? or a another way to overcome this problem besides Masking?