I don't know why it took me so long...it was actually quite easy. I just used double sided hem tape.
Look, I even mitered the corners with some creative folding and fabric glue!
(Btw, here's the link to the shade I purchased. It isn't the highest quality, but it was on sale and super cheap. I think with shipping I ended up paying around 20 bucks.)
Here's what it looks like in the room after the Hubs hung it for me.
Just the perfect custom touch for our powder room.