If it's a smaller window you could remove the backing paper entirely.

如果窗户较小，你可以将贴膜背面的纸全部撕掉。

youdao

Backing paper: a base layer to give strength or support to a top layer.

托底纸：用来支撑面层的纸以啬强度或承托面层。

youdao

Backing paper: a base layer to give strength or support to a top layer.

托底纸：用来支撑面层的纸以啬强度或承托面层。

youdao